cp's OEIS Frontend

A226147 Numbers n such that triangular(n) is an average of three successive primes.

%I A226147 #5 May 29 2013 12:16:50
%S A226147 193,233,265,301,526,709,753,922,961,962,986,1126,1178,1285,1373,1485,
%T A226147 1525,1537,1558,1601,1710,1737,1962,1965,2202,2437,2466,2578,2685,
%U A226147 2693,2862,3206,3346,3462,3622,3682,3937,3938,3965,4005,4017,4018,4058,4393,4489,4498,4717
%N A226147 Numbers n such that triangular(n) is an average of three successive primes.
%o A226147 (C)
%o A226147 #include <stdio.h>
%o A226147 #include <stdlib.h>
%o A226147 #include <math.h>
%o A226147 #define TOP (1ULL<<30)
%o A226147 int main() {
%o A226147   unsigned long long i, j, p1, p2, r, s;
%o A226147   unsigned char *c = (unsigned char *)malloc(TOP/8);
%o A226147   memset(c, 0, TOP/8);
%o A226147   for (i=3; i < TOP; i+=2)
%o A226147     if ((c[i>>4] & (1<<((i>>1) & 7)))==0 /*&& i<(1ULL<<32)*/)
%o A226147         for (j=i*i>>1; j<TOP; j+=i)  c[j>>3] |= 1 << (j&7);
%o A226147   for (p2=2, p1=3, i=5; i < TOP; i+=2)
%o A226147     if ((c[i>>4] & (1<<((i>>1) & 7)))==0) {
%o A226147       s = p2 + p1 + i;
%o A226147       if ((s%3)==0) {
%o A226147         s/=3;
%o A226147         r = sqrt(s*2);
%o A226147         if (r*(r+1)==s*2) printf("%llu, ", r);
%o A226147       }
%o A226147       p2 = p1, p1 = i;
%o A226147     }
%o A226147   return 0;
%o A226147 }
%Y A226147 Cf. A076304, A206279, A226145-A226150.
%K A226147 nonn
%O A226147 1,1
%A A226147 _Alex Ratushnyak_, May 28 2013