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A226147 Numbers n such that triangular(n) is an average of three successive primes. 2
193, 233, 265, 301, 526, 709, 753, 922, 961, 962, 986, 1126, 1178, 1285, 1373, 1485, 1525, 1537, 1558, 1601, 1710, 1737, 1962, 1965, 2202, 2437, 2466, 2578, 2685, 2693, 2862, 3206, 3346, 3462, 3622, 3682, 3937, 3938, 3965, 4005, 4017, 4018, 4058, 4393, 4489, 4498, 4717 (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*2);

        if (r*(r+1)==s*2) printf("%llu, ", r);

      }

      p2 = p1, p1 = i;

    }

  return 0;

}

CROSSREFS

Cf. A076304, A206279, A226145-A226150.

Sequence in context: A114859 A298728 A088119 * A142925 A060333 A020352

Adjacent sequences:  A226144 A226145 A226146 * A226148 A226149 A226150

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, May 28 2013

STATUS

approved

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Last modified March 20 15:43 EDT 2019. Contains 321345 sequences. (Running on oeis4.)