A226501 Triangular numbers that are the product of 4 distinct triangular numbers greater than 1.

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

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