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

2,1

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

Crossrefs

Cf. A001819, A002701, A007406.

Sequence in context: A189241 A167205 A123781 * A178342 A117751 A093526

Adjacent sequences: A120295 A120296 A120297 * A120299 A120300 A120301

Keyword

nonn

Author

Alexander Adamchuk, Jul 11 2006

Extensions

More terms from Daniel Suteu, Jun 10 2022

Status

approved