A081950 Smallest triangular number k such that k-1 has exactly n (not necessarily distinct) prime factors.

3, 10, 21, 55, 253, 325, 1081, 4753, 8001, 18145, 226801, 293761, 7378561, 1181953, 33566721, 184291201, 471905281, 75479041, 924908545, 4831985665, 8590131201, 137438167041, 146163916801, 1051224625153, 309236465665, 19791199862785

Offset

1,1

Links

Table of n, a(n) for n=1..26.

Example

a(4) = 2*3*3*3+1 = 55.

Crossrefs

Cf. A081951.

Sequence in context: A008837 A176098 A355389 * A204340 A331017 A207646

Adjacent sequences: A081947 A081948 A081949 * A081951 A081952 A081953

Keyword

nonn

Author

Amarnath Murthy, Apr 02 2003

Extensions

Extended and edited by Ryan Propper, Jun 21 2005

a(24)-a(26) from Donovan Johnson, Jan 31 2009

Status

approved