A151611 a(1) = 4; for n >= 1, a(n+1) = 4 + binomial(a(n), 2).

4, 10, 49, 1180, 695614, 241939070695, 29267256964259134356169, 428286165105987400438217763289707431507000200

Offset

1,1

Comments

Arises in a geometry problem: see link.

Next term (a(9)) has 89 digits. - Emeric Deutsch, Jun 20 2009

Links

Table of n, a(n) for n=1..8.

Antreas P. Hatzipolakis, Concurrent NPC's.

Antreas P. Hatzipolakis, Concurrent NPCs, digest of 4 messages in Anopolis Yahoo group, May 23, 2009 - Aug 26, 2016. [Cached copy]

Maple

a[1] := 4: for n to 7 do a[n+1] := 4+binomial(a[n], 2) end do: seq(a[n], n = 1 .. 8); # Emeric Deutsch, Jun 20 2009

Prog

(Magma) [n eq 1 select 4 else 4+Binomial(Self(n-1), 2):n in [1..8]]; // Marius A. Burtea, Nov 16 2019

Crossrefs

Sequence in context: A364281 A173086 A081565 * A351046 A208236 A032495

Adjacent sequences: A151608 A151609 A151610 * A151612 A151613 A151614

Keyword

nonn,easy

Author

N. J. A. Sloane, May 28 2009

Extensions

More terms from Emeric Deutsch, Jun 20 2009

Status

approved