A076170 Triangular numbers whose largest proper divisor is also triangular.

1, 3, 6, 45, 210, 7140, 122265, 242556, 1702935, 8239770, 279909630, 4601330415, 9508687656, 64088265153, 323015470680, 10973017315470, 173166468725253, 372759573255306, 2411897769074475, 12662852473364940, 430164224521152660, 6516946879404850395

Offset

1,2

Comments

No more terms < 10^16. - David Wasserman, Apr 05 2005

2^63 < a(23) <= 14612920781245825506. - Donovan Johnson, Apr 24 2011

Links

Table of n, a(n) for n=1..22.

Prog

(PARI) isTriang(n) = local(x); x = sqrtint(2*n); n == x*(x + 1)/2;
i = 1; n = 1; print1(n, ", "); while(1, i++; n += i; f = factor(n); if (isTriang(n/f[1, 1]), print1(n, ", "))); \\ David Wasserman, Apr 05 2005

Crossrefs

Sequence in context: A009581 A088674 A203434 * A137775 A038050 A194080

Adjacent sequences: A076167 A076168 A076169 * A076171 A076172 A076173

Keyword

nonn

Author

Jason Earls, Nov 01 2002

Extensions

More terms from David Wasserman, Apr 05 2005

a(20)-a(22) from Donovan Johnson, Apr 24 2011

Status

approved