cp's OEIS Frontend

A226102 Prime powers (A025475) representable as triangular(k)+1.

%I A226102 #14 May 29 2013 12:14:54
%S A226102 1,4,16,121,529,4096,139129,160554241,812293020529,
%T A226102 379188080252621270252095321
%N A226102 Prime powers (A025475) representable as triangular(k)+1.
%C A226102 Indices of triangular numbers are in A226103.
%C A226102 53072032161200090602953513048447623^2 is also a term. - _Giovanni Resta_, May 26 2013
%F A226102 a(n) = A000217(A226103(n)) + 1.
%o A226102 (C)
%o A226102 #include <stdio.h>
%o A226102 #include <stdlib.h>
%o A226102 #include <math.h>
%o A226102 #define TOP (1ULL<<32)  // Memory usage: 0.5 Gb
%o A226102 int main() {
%o A226102   unsigned long long i, j, p, t, r;
%o A226102   unsigned char *c = (unsigned char *)malloc(TOP/8);
%o A226102   memset(c, 0, TOP/8);
%o A226102   for (printf("1, "), i=1; i < TOP; i+=2)
%o A226102     if ((c[i>>4] & (1<<((i>>1)&7))) == 0) {
%o A226102       for (p = i + (i==1), j = p*p; ; j*=p) {
%o A226102         t = j - 1;
%o A226102         r = sqrt(t*2);
%o A226102         if (r*(r+1)==t*2)  printf("%llu, ", j);
%o A226102         double k = ((double)j) * ((double)p);
%o A226102         if (k >= ((double)(1ULL<<62)*4.0)) break;
%o A226102       }
%o A226102       if (i>1) for (j=i*i>>1; j<TOP; j+=i)  c[j>>3] |= 1 << (j&7);
%o A226102     }
%o A226102   // SORT the output
%o A226102   return 0;
%o A226102 }
%Y A226102 Cf. A025475, A000217, A226103.
%K A226102 nonn,more
%O A226102 1,2
%A A226102 _Alex Ratushnyak_, May 26 2013
%E A226102 a(10) from _Giovanni Resta_, May 26 2013