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

Author

M. F. Hasler, Nov 11 2006

Keywords

• nonn

Comments

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

Examples

			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.
		

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)

Crossrefs

Cf. A007408, A124876, A124877.

Programs

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 *)

Formula

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

Extensions

Data corrected and extended by Amiram Eldar, Feb 09 2020