A099179 Iterated tetrahedral numbers.

2, 4, 20, 1540, 609896980, 37811003218473324699257860, 9009555207802177724984164589516456320805205201729086740415363658290866918420

Offset: 1

Author

Jonathan Vos Post, Nov 15 2004

Keywords

• easy
• nonn

Comments

The next term, a(8), has 228 digits. - Harvey P. Dale, Dec 18 2012

Examples

			a(2) = Tet(2) = the 2nd tetrahedral number = 2*(2+1)*(2+2)/6 = 4;
a(3) = Tet(Tet(2)) = the 4th tetrahedral number = 4*(4+1)*(4+2)/6 = 20;
a(4) = Tet(Tet(Tet(2))) = the 20th tetrahedral number = 20*(20+1)*(20+2)/6 = 1540.
		

Links

• Eric Weisstein's World of Mathematics, Tetrahedral Number.

Crossrefs

Cf. A007501, A000292.

Programs

Mathematica

NestList[(#(#+1)(#+2))/6&,2,6] (* Harvey P. Dale, Dec 18 2012 *)

Formula

a(n)= A000292(a(n-1)). - R. J. Mathar, Jun 09 2008

Extensions

Corrected and extended by R. J. Mathar, Jun 09 2008