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A226501 Triangular numbers that are the product of 4 distinct triangular numbers greater than 1. 0
25200, 97020, 145530, 499500, 673380, 749700, 839160, 1185030, 1445850, 1786995, 1873080, 2031120, 2049300, 2162160, 2821500, 3444000, 3646350, 4250070, 4573800, 4915680, 4991220, 5364450, 5512860, 6193440, 11594520, 11763675, 12748725, 13857480, 14340690, 15481830 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..30.

PROG

(C)

#include <stdio.h>

#include <math.h>

typedef unsigned long long U64;

U64 isTriangular(U64 a) {  // ! Must be a < (1<<63)

    U64 s = sqrt(a*2);

    if (a>=(1ULL<<63)) exit(1);

    return (s*(s+1) == a*2);

}

int compare64(const void *p1, const void *p2) {

  if (*(U64*)p1 == *(U64*)p2) return 0;

  return (*(U64*)p1 < *(U64*)p2) ? -1 : 1;

}

#define TOP (1ULL<<19)

U64 d[TOP];

int main() {

  U64 n, x, tx, y, ty, z, tz, w, tw, p = 0;

  for (x = tx = 3; tx <= TOP; tx+=x, ++x) {

  for (y = ty = 3; ty < tx;   ty+=y, ++y) {

  for (z = tz = 3; tz < ty;   tz+=z, ++z) {

  for (w = tw = 3; tw < tz;   tw+=w, ++w) {

    n = tx*ty*tz;

    if (n<TOP*180 && (n*=tw)<TOP*180 && isTriangular(n))

      d[p++] = n;

  }}}}

  qsort(d, p, 8, compare64);

  for (x=n=0; n<p; ++n)

    if (d[n] > x)  x = d[n], printf("%llu, ", x);

  return 0;

}

CROSSREFS

Cf. A000217, A225440.

Sequence in context: A190319 A296097 A076583 * A046709 A179723 A174825

Adjacent sequences:  A226498 A226499 A226500 * A226502 A226503 A226504

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Jun 09 2013

STATUS

approved

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Last modified August 3 14:40 EDT 2021. Contains 346438 sequences. (Running on oeis4.)