Sum of two adjacent numbers are primes: Difference between revisions

=={{header|ALGOL 68}}==

{{libheader|ALGOL 68-primes}}

<lang algol68>BEGIN # find the first 20 primes which are n + ( n + 1 ) for some n #

PR read "primes.incl.a68" PR # include prime utilities #

[]BOOL prime = PRIMESIEVE 200; # should be enough primes #

INT p count := 0;

FOR n WHILE p count < 20 DO

INT n1 = n + 1;

INT p = n + n1;

IF prime[ p ] THEN

p count +:= 1;

print( ( whole( n, -2 ), " + ", whole( n1, -2 ), " = ", whole( p, -3 ), newline ) )

FI

OD

END</lang>

{{out}}

<pre>

1 + 2 = 3

2 + 3 = 5

3 + 4 = 7

5 + 6 = 11

6 + 7 = 13

8 + 9 = 17

9 + 10 = 19

11 + 12 = 23

14 + 15 = 29

15 + 16 = 31

18 + 19 = 37

20 + 21 = 41

21 + 22 = 43

23 + 24 = 47

26 + 27 = 53

29 + 30 = 59

30 + 31 = 61

33 + 34 = 67

35 + 36 = 71

36 + 37 = 73

</pre>