A385146 Pentagonal numbers that are five times another pentagonal number.

0, 5, 11310, 55089888425, 121583358792810, 592213938425857857485, 1307015893771450525626150, 6366274445128720143976790614385, 14050364815815600018103892686892130, 68437177312018083317895951729386272287125, 151040819318475127652012254231608319757368350

Offset

1,2

Links

Table of n, a(n) for n=1..11.

Formula

a(n) = 5 * A385152(n).

Example

P = 11310 is a term since P and P/5 = 2262 are both pentagonal numbers.

Prog

(PARI) is_a000326(n) = my(s); n==0 || (issquare (24*n+1, &s) && s%6==5);
for(n=0, oo, p=n*(3*n-1)/2; if(p%5==0 && is_a000326(p/5), print1(p, ", "))); \\ Joerg Arndt, Jun 19 2025

Crossrefs

Cf. A000326, A076140, A385152.

Sequence in context: A376103 A260262 A058051 * A242772 A368067 A364691

Adjacent sequences: A385143 A385144 A385145 * A385147 A385148 A385149

Keyword

nonn

Author

Kelvin Voskuijl, Jun 19 2025

Status

approved