Sum of primes in odd positions is prime: Difference between revisions

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 {{libheader|ALGOL 68-primes}}
 <lang algol68>BEGIN  # find primes (up to 999) p(i) for odd i such that the sum of primes p(j), j = 1, 3, 5, ..., i is prime #
-    INT max prime = 999;
     PR read "primes.incl.a68" PR
+    INT max prime    = 999;
-    []BOOL prime = PRIMESIEVE 50 000; # guess that the max sum will be <= 50 000 #
+    []BOOL prime     = PRIMESIEVE 50 000;                                # guess that the max sum will be <= 50 000 #
-    # count the primes up to max prime #
-    INT p count := 0; FOR i TO max prime DO IF prime[ i ] THEN p count +:= 1 FI OD;
+    []INT  low prime = EXTRACTPRIMESUPTO max prime FROMPRIMESIEVE prime; # get a list of primes up to max prime     #
-    # construct a list of the primes up to max prime #
-    [ 1 : p count ]INT low prime;
-    INT low pos := 0;
-    FOR i TO max prime DO IF prime[ i ] THEN low prime[ low pos +:= 1 ] := i FI OD;
     # find the sums of the odd primes and test for primality #
     print( ( "  i p[i]    sum", newline ) );