Truncatable primes: Difference between revisions
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m →{{header|REXX}}: made REXX code compliant, added DO-END comment labels, removed two blank lines, added other whitespace. -- ~~~~ |
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=={{header|REXX}}== |
=={{header|REXX}}== |
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| ⚫ | |||
<lang REXX> |
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| ⚫ | |||
x.=0 /*placeholders for primes. */ |
x.=0 /*placeholders for primes. */ |
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p.=999 /*default value for P.n */ |
p.=999 /*default value for P.n */ |
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/*the above 4 lines saves time*/ |
/*the above 4 lines saves time*/ |
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do k=6 /*divide by known odd primes. */ |
do k=6 /*divide by known odd primes. */ |
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if p.k**2>j then leave |
if p.k**2>j then leave /*only go up to sqrt(J). */ |
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if j//p.k==0 then iterate j /*divisible by X? Not prime. */ |
if j//p.k==0 then iterate j /*divisible by X? Not prime. */ |
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end |
end /*k*/ |
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n=n+1 /*bump number of primes found.*/ |
n=n+1 /*bump number of primes found.*/ |
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p.n=j /*assign to sparse array. */ |
p.n=j /*assign to sparse array. */ |
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x.j=1 /*indicate that J is a prime. */ |
x.j=1 /*indicate that J is a prime. */ |
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end |
end /*j*/ |
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say 'The last prime is' p.n "("n 'primes under one million).' |
say 'The last prime is' p.n "("n 'primes under one million).' |
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do j=1 for n /*find left-trunc. primes. */ |
do j=1 for n /*find left-trunc. primes. */ |
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y=p.j; g=y |
y=p.j; g=y |
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if pos(0,y)\==0 then iterate /*if prime contains a 0, nope.*/ |
if pos(0,y)\==0 then iterate /*if prime contains a 0, nope.*/ |
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do k=1 for length(y)-1 /*test for prime, skip whole #*/ |
do k=1 for length(y)-1 /*test for prime, skip whole #*/ |
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g=right(y,k); if \x.g then iterate j |
g=right(y,k); if \x.g then iterate j |
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end |
end /*k*/ |
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lp=max(lp,y) /*choose the maximum so far. */ |
lp=max(lp,y) /*choose the maximum so far. */ |
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end |
end /*j*/ |
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rp=0 |
rp=0 |
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do j=1 for n /*find left-trunc. primes. */ |
do j=1 for n /*find left-trunc. primes. */ |
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y=p.j; g=y |
y=p.j; g=y |
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if pos(0,y)\==0 then iterate /*if prime contains a 0, nope.*/ |
if pos( 0,y)\==0 then iterate /*if prime contains a 0, nope.*/ |
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do k=1 for length(y)-1 /*test for prime, skip whole #*/ |
do k=1 for length(y)-1 /*test for prime, skip whole #*/ |
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g=left(y,k); if \x.g then iterate j |
g=left(y,k); if \x.g then iterate j |
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end |
end /*k*/ |
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rp=max(rp,y) /*choose the maximum so far. */ |
rp=max(rp,y) /*choose the maximum so far. */ |
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end |
end /*j*/ |
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say 'The largest left-truncatable prime is' lp '(under one million).' |
say 'The largest left-truncatable prime is' lp '(under one million).' |
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say 'The largest right-truncatable prime is' rp '(under one million).' |
say 'The largest right-truncatable prime is' rp '(under one million).'</lang> |
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'''output''' |
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</lang> |
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Output: |
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<pre> |
<pre> |
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The last prime is 999983 (78498 primes under one million). |
The last prime is 999983 (78498 primes under one million). |
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