A145272 First differences of successive iterated triangular numbers with seed 2.

1, 3, 15, 210, 26565, 358999410, 64449908117864115, 2076895351339769396027702893296360, 2156747150208372213435450937462080290024600343143329179374709804540

Offset

1,2

Comments

Also a triangular number -- follows from the definition of A007501.

Links

Table of n, a(n) for n=1..9.

Formula

a(n) = T(x(n-1))-x(n-1) where x(n)=T(x(n-1)) and T(x)=x*(x+1)/2.

Example

a(1)=T(2)-2.
a(2)=T(3)-3.
a(3)=T(6)-6.

Crossrefs

First differences of successive terms of sequence A007501.

Cf. A000217.

Sequence in context: A003505 A270354 A120601 * A264705 A117820 A126453

Adjacent sequences: A145269 A145270 A145271 * A145273 A145274 A145275

Keyword

easy,nonn

Author

Greg Huber, Oct 06 2008

Status

approved