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A225400
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First occurrence of n in A225399, or -1 if n does not appear in A225399.
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2
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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
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OFFSET
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0,2
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COMMENTS
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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.
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LINKS
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FORMULA
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A000217(a(n)) = A076983(n+1) for n>0, if the conjecture is true and a(n) >= 0.
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MATHEMATICA
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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 *)
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PROG
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(C)
#include <stdio.h>
#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<TOP && f[c]<0)
for (printf("\n"), f[c]=i, j=0; j<TOP; ++j)
printf("%lld, ", f[j]);
}
return 0;
}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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