A099137 Iterated pentagonal numbers starting with 2.

2, 5, 35, 1820, 4967690, 37016913420305, 2055377818749516111922729385, 6336866966711278058881411525857304983854251425952352645

Offset

0,1

Links

Table of n, a(n) for n=0..7.

Eric Weisstein's World of Mathematics, Pentagonal Number

Formula

Let P(n) = n*(3*n-1)/2, a(1) = 2 and a(n) = P(a(n-1)) for n >= 2.

Prog

(PARI) a(n)=if(n==1, 2, a(n-1)*(3*a(n-1)-1)/2); \\ Joerg Arndt, Mar 05 2023

Crossrefs

Cf. A007501, A000326.

Sequence in context: A350955 A193323 A238752 * A309667 A059586 A160968

Adjacent sequences: A099134 A099135 A099136 * A099138 A099139 A099140

Keyword

easy,nonn

Author

Jonathan Vos Post, Nov 14 2004

Extensions

Edited by Giovanni Resta, Jun 17 2016

Edited by Joerg Arndt, Mar 05 2023

Status

approved