Summarize primes: Difference between revisions
Added Algol W
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END</lang>
{{out}}
<pre>
prime prime
count sum
1 2
2 5
4 17
6 41
12 197
14 281
60 7699
64 8893
96 22039
100 24133
102 25237
108 28697
114 32353
122 37561
124 38921
130 43201
132 44683
146 55837
152 61027
158 66463
162 70241
Found 21 prime sums of primes below 1000
</pre>
=={{header|ALGOL W}}==
<lang algolw>begin % sum the primes below n and report the sums that are prime %
integer MAX_NUMBER;
MAX_NUMBER := 999;
begin
logical array prime( 1 :: MAX_NUMBER );
integer primeCount, primeSum, primeSumCount;
% sieve the primes to MAX_NUMBER %
prime( 1 ) := false; prime( 2 ) := true;
for i := 3 step 2 until MAX_NUMBER do prime( i ) := true;
for i := 4 step 2 until MAX_NUMBER do prime( i ) := false;
for i := 3 step 2 until truncate( sqrt( MAX_NUMBER ) ) do begin
integer ii; ii := i + i;
if prime( i ) then begin
for p := i * i step ii until MAX_NUMBER do prime( p ) := false
end if_prime_i
end for_i ;
% find the prime sums that are prime %
primeCount := primeSum := primeSumCount := 0;
write( "prime prime" );
write( "count sum" );
for i := 1 until MAX_NUMBER do begin
if prime( i ) then begin
% have another prime %
logical isPrime;
primeSum := primeSum + i;
primeCount := primeCount + 1;
% check whether the prime sum is also prime %
isPrime := true;
for p := 1 until i div 2 do begin
if prime( p ) then begin
isPrime := primeSum rem p not = 0;
if not isPrime then goto endPrimeCheck
end if_prime_p
end for_p ;
endPrimeCheck:
if isPrime then begin
% the prime sum is also prime %
primeSumCount := primeSumCount + 1;
write( i_w := 5, s_w := 0
, primeCount
, " "
, i_w := 6
, primeSum
)
end if_isPrime
end if_prime_i
end for_i ;
write();
write( i_w := 1, s_w := 0
, "Found "
, primeSumCount
, " prime sums of primes below "
, MAX_NUMBER + 1
)
end
end.</lang>
{{out}}
<pre>
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