Palindromic primes: Difference between revisions
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Generates the palindrmic 3 digit numbers and uses the observations that all 1 digit primes are palindromic and that for 2 digit numbers, only multiples of 11 are palindromic and hence 11 is the only two digit palindromic prime. |
Generates the palindrmic 3 digit numbers and uses the observations that all 1 digit primes are palindromic and that for 2 digit numbers, only multiples of 11 are palindromic and hence 11 is the only two digit palindromic prime. |
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{{libheader|ALGOL 68-primes}} |
{{libheader|ALGOL 68-primes}} |
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<syntaxhighlight lang="algol68">BEGIN # find primes that are palendromic in base 10 # |
<syntaxhighlight lang="algol68">BEGIN # find primes that are palendromic in base 10 # |
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INT max prime = 999; |
INT max prime = 999; |
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# sieve the primes to max prime # |
# sieve the primes to max prime # |
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PR read "primes.incl.a68" PR |
PR read "primes.incl.a68" PR |
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[]BOOL prime = PRIMESIEVE max prime; |
[]BOOL prime = PRIMESIEVE max prime; |
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# print the palendromic primes in the base 10 # |
# print the palendromic primes in the base 10 # |
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# all 1 digit primes are palindromic # |
# all 1 digit primes are palindromic # |
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# the only palindromic 2 digit numbers are multiples of 11 # |
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# the only |
# so 11 is the only possible 2 digit palindromic prime # |
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# so 11 is the only possible 2 digit palindromic prime # |
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# three digit numbers, the first and last digits must be odd # |
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# |
# and cannot be 5 (as the number would be divisible by 5) # |
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# and cannot be 5 (as the number would be divisible by 5) # |
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FOR fl BY 2 TO 9 DO |
FOR fl BY 2 TO 9 DO |
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IF fl /= 5 THEN |
IF fl /= 5 THEN |
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OD; |
OD; |
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print( ( newline ) ) |
print( ( newline ) ) |
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END |
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</syntaxhighlight> |
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{{out}} |
{{out}} |
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<pre> |
<pre> |
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