A120298 Largest prime factor of the n-th central factorial number A001819(n).

5, 7, 41, 479, 59, 266681, 63397, 514639, 178939, 242101, 18500393, 40799043101, 190297, 1844659, 78206663, 616798327, 38512247, 86364397717734821, 421950627598601, 84786899, 52030193, 31411862913089, 1422157053067, 47961582392203, 8408339, 6269019298981

Offset: 2

Author

Alexander Adamchuk, Jul 11 2006

Keywords

• nonn

Links

• Daniel Suteu, Table of n, a(n) for n = 2..180

Crossrefs

Cf. A001819, A002701, A007406.

Programs

Mathematica

Table[Max[FactorInteger[Sum[1/i^2,{i,1,n}]/Product[1/i^2,{i,1,n}]]],{n,2,30}]
Table[FactorInteger[n!^2*HarmonicNumber[n,2]][[-1,1]],{n,2,30}] (* Harvey P. Dale, Jul 29 2023 *)

PARI

a(n) = vecmax(factor(n!^2 * sum(k=1, n, 1/k^2))[,1]); \\ Daniel Suteu, Jun 10 2022

Formula

a(n) = A006530(A001819(n)). - Daniel Suteu, Jun 10 2022

Extensions

More terms from Daniel Suteu, Jun 10 2022