A225536 Numbers of triples {x, y, z} such that z >= y > 1 and prime(x) + prime(y) * prime(z) = 2^n.

0, 0, 0, 0, 1, 4, 5, 15, 22, 43, 65, 131, 204, 387, 635, 1136, 2048, 3727, 6794, 12296, 22601, 41746, 76778, 141923, 263414, 491925, 917269, 1718985, 3225496, 6067030, 11435208, 21593415, 40858139

Offset: 0

Author

Alex Ratushnyak, May 10 2013

Keywords

• nonn
• more

Examples

			2^4 = 16 = 7 + 3*3, so a(4) = 1.
2^5 = 32 = 7 + 5*5 = 11 + 3*7 = 17 + 3*5 = 23 + 3*3, so a(5) = 4.
		

Crossrefs

Cf. A000040, A006307, A225437.

Programs

C

#include 
#include 
#define TOP (1ULL<<32)
int main() {
  unsigned long long i, j, k, n, pp = 0, x, px, y, py, sr;
  unsigned int *primes = (unsigned int*)malloc(TOP/4);
  char *c = (char*)malloc(TOP/2);
  memset(c, 0, TOP/2);
  for (c[0] = i = 3; i < TOP; i+=2)
    if (c[i>>1]==0)
      for (primes[pp++]=i, j=i*i>>1; j>1] == 0) ++k; break; }
    }
    printf("%llu, ", k);
  }
}