OFFSET
0,1
LINKS
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.
MATHEMATICA
NestList[PolygonalNumber[5, #]&, 2, 8] (* Harvey P. Dale, Sep 07 2024 *)
PROG
(PARI) a(n)=if(n==1, 2, a(n-1)*(3*a(n-1)-1)/2); \\ Joerg Arndt, Mar 05 2023
CROSSREFS
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