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A076170
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Triangular numbers whose largest proper divisor is also triangular.
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0
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1, 3, 6, 45, 210, 7140, 122265, 242556, 1702935, 8239770, 279909630, 4601330415, 9508687656, 64088265153, 323015470680, 10973017315470, 173166468725253, 372759573255306, 2411897769074475, 12662852473364940, 430164224521152660, 6516946879404850395
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| No more terms < 10^16. - David Wasserman (wasserma(AT)spawar.navy.mil), Apr 05 2005
2^63 < a(23) <= 14612920781245825506. - Donovan Johnson, Apr 24 2011
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PROG
| (PARI) isTriang(n) = local(x); x = sqrtint(2*n); n == x*(x + 1)/2; i = 1; n = 1; while(1, i++; n += i; f = factor(n); if (isTriang(n/f[1, 1]), print(n))); (Wasserman)
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CROSSREFS
| Sequence in context: A009581 A088674 A203434 * A137775 A038050 A194080
Adjacent sequences: A076167 A076168 A076169 * A076171 A076172 A076173
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Nov 01 2002
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EXTENSIONS
| More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Apr 05 2005
a(20)-a(22) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Apr 24 2011
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