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A226146 Numbers n such that n^2 is an average of three successive primes. 1
49, 161, 219, 351, 363, 469, 575, 597, 671, 877, 909, 933, 1013, 1225, 1231, 1303, 1359, 1381, 1419, 1489, 1577, 1653, 1797, 1815, 1989, 2083, 2117, 2177, 2241, 2289, 2301, 2403, 2483, 2493, 2517, 2611, 2617, 2653, 2727, 2779, 2869, 2931, 3029, 3051, 3261, 3515, 3617 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..47.

PROG

(C)

#include <stdio.h>

#include <stdlib.h>

#include <math.h>

#define TOP (1ULL<<30)

int main() {

  unsigned long long i, j, p1, p2, r, s;

  unsigned char *c = (unsigned char *)malloc(TOP/8);

  memset(c, 0, TOP/8);

  for (i=3; i < TOP; i+=2)

    if ((c[i>>4] & (1<<((i>>1) & 7)))==0 /*&& i<(1ULL<<32)*/)

        for (j=i*i>>1; j<TOP; j+=i)  c[j>>3] |= 1 << (j&7);

  for (p2=2, p1=3, i=5; i < TOP; i+=2)

    if ((c[i>>4] & (1<<((i>>1) & 7)))==0) {

      s = p2 + p1 + i;

      if ((s%3)==0) {

        s/=3;

        r = sqrt(s);

        if (r*r==s) printf("%llu, ", r);

      }

      p2 = p1, p1 = i;

    }

  return 0;

}

CROSSREFS

Cf. A076304, A206279, A226145-A226150.

Sequence in context: A044762 A159247 A265423 * A066551 A134210 A009409

Adjacent sequences:  A226143 A226144 A226145 * A226147 A226148 A226149

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, May 28 2013

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.