A124875 Greatest prime dividing A007408(n).

3, 251, 37, 5449, 53, 2591, 2538983, 462191, 4957, 5042929, 151099201553, 119465070161, 8868751511, 56154295334575853, 4480577578703, 1254664312327399, 34237559, 1683118856778495358491487, 294307265949353, 46956374669685791, 46572151, 110732345922475922393023393

Offset

2,1

Comments

For all n>2, the exponent of a(n) in the factorization of A007408(n) appears to be 1.

Links

Sean A. Irvine, Table of n, a(n) for n = 2..131 (a(50) corrected, Mar 14 2023, terms 2..106 from Amiram Eldar)

Formula

a(n) = A006530(A007408(n)). - Amiram Eldar, Feb 09 2020

Example

The offset is 2 since A007408(1) = 1 has no prime divisors at all.
a(2) = 3 is the largest prime dividing A007408(2) = 9,
a(3) = 251 is the largest prime dividing A007408(3) = 251,
a(4) = 37 since A007408(4) = 5 * 11 * 37.

Maple

seq(op([ -1, -2], op(-1, ifactors(A007408(n)))), n=2..25);

Mathematica

Table[FactorInteger[Numerator[Sum[1/k^3, {k, 1, n}]]][[-1, 1]], {n, 2, 20}] (* Amiram Eldar, Feb 09 2020 *)

Crossrefs

Cf. A007408, A124876, A124877.

Sequence in context: A157777 A318065 A349644 * A226986 A158351 A025418

Adjacent sequences: A124872 A124873 A124874 * A124876 A124877 A124878

Keyword

nonn

Author

M. F. Hasler, Nov 11 2006

Extensions

Data corrected and extended by Amiram Eldar, Feb 09 2020

Status

approved