A225399 -id:A225399 - cp's OEIS frontend

A225400 First occurrence of n in A225399, or -1 if n does not appear in A225399.

0, 3, 8, 14, 15, 39, 20, 44, 35, 195, 119, 104, 594, 224, 384, 455, 539, 440, 560, 3080, 2184, 1539, 2015, 2639, 5264, 4199, 15399, 13299, 8855, 23919, 2079, 30744, 43680, 36575, 14399, 5984, 58695, 113399, 47124, 107184, 12375, 78624, 98175, 73359, 111320, 242879

Offset: 0

Alex Ratushnyak, May 06 2013

nonn

Index of the least triangular number t divisible by exactly n triangular numbers bigger than 1 and less than t, or -1 if there is no such t.

Conjecture: a(n) >= 0.

Cf. A000217, A225399, A076983.

#include 
#define TOP 80
int main() {
  unsigned long long c, i, j, t, tn;
  long long f[TOP];
  memset(f, -1, sizeof(f));
  for (i = tn = 0; i < (1ULL<<32); i++) {
        for (c=0, tn += i, t = j = 3; t*2 <= tn; t+=j, ++j)
                if (tn%t==0) ++c;
        if (c

mx = 10000; tri = Table[n (n + 1)/2, {n, mx}]; nn = 20; t = Table[0, {nn}]; found = 0; n = 0; While[n < mx && found < nn, n++; cnt = 0; Do[If[Mod[tri[[n]], tri[[k]]] == 0, cnt++], {k, 2, n - 1}]; If[cnt <= nn && t[[cnt]] == 0, t[[cnt]] = n; found++]]; Join[{0}, t] (* T. D. Noe, May 07 2013 *)

A000217(a(n)) = A076983(n+1) for n>0, if the conjecture is true and a(n) >= 0.

cp's OEIS Frontend

A225400 First occurrence of n in A225399, or -1 if n does not appear in A225399.

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