A120298 - OEIS

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

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OFFSET

2,1

LINKS

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

FORMULA

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

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 *)

PROG

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