Sum of two adjacent numbers are primes: Difference between revisions
Sum of two adjacent numbers are primes (view source)
Revision as of 14:07, 18 December 2022
, 1 year agoAdded Algol W
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(Added Algol W) |
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Line 97:
35 + 36 = 71
36 + 37 = 73
</pre>
=={{header|ALGOL W}}==
<syntaxhighlight lang="algolw">
begin % find numbers n such that n + n+1 is prime %
% sets s to a sieve of primes, using the sieve of Eratosthenes %
procedure sieve( logical array s ( * ); integer value n ) ;
begin
% start with everything flagged as prime %
for i := 1 until n do s( i ) := true;
% sieve out the non-primes %
s( 1 ) := false;
for i := 2 until truncate( sqrt( n ) )
do begin
if s( i )
then begin
for p := i * i step i until n do s( p ) := false
end if_s_i
end for_i ;
end sieve ;
integer sieveMax;
sieveMax := 200;
begin
logical array prime ( 1 :: sieveMax );
integer count, n, n1;
i_w := 2; % set output integer field width %
s_w := 1; % and output separator width %
% find and display the numbers %
sieve( prime, sieveMax );
count := 0;
n1 := 1;
while count < 20 do begin
n := n1;
n1 := n1 + 1;
if prime( n + n1 ) then begin
count := count + 1;
write( count, ": ", n, " + ", n1, " = ", n + n1 )
end if_prime__n_plus_n1
end while_count_lt_20
end
end.
</syntaxhighlight>
{{out}}
<pre>
1 : 1 + 2 = 3
2 : 2 + 3 = 5
3 : 3 + 4 = 7
4 : 5 + 6 = 11
5 : 6 + 7 = 13
6 : 8 + 9 = 17
7 : 9 + 10 = 19
8 : 11 + 12 = 23
9 : 14 + 15 = 29
10 : 15 + 16 = 31
11 : 18 + 19 = 37
12 : 20 + 21 = 41
13 : 21 + 22 = 43
14 : 23 + 24 = 47
15 : 26 + 27 = 53
16 : 29 + 30 = 59
17 : 30 + 31 = 61
18 : 33 + 34 = 67
19 : 35 + 36 = 71
20 : 36 + 37 = 73
</pre>
Line 153 ⟶ 221:
36 + 37 = 73
</pre>
=={{header|BASIC}}==
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