A290051 Least k > 1 such that the set of distinct prime divisors of k is equal to the set of distinct prime divisors of sigma_n(k) where sigma_n (k) is result of applying sum-of-divisors function n times to k.

6, 2, 294, 2, 126, 112, 310, 14, 150, 840, 3200, 98, 45360, 10500, 57120, 40320, 242250, 9548, 21839790, 3756480, 200425680, 678810, 1359540

Offset

1,1

Comments

a(24) > 10^9.

Links

Table of n, a(n) for n=1..23.

Example

a(3) = 294 because sigma(sigma(sigma(2*3*7^2))) = 2^5*3*7^2 and 2*3*7^2 = 294 is the least number with this property.

Mathematica

f[n_] := Block[{k = 2}, While[ Transpose[ FactorInteger[ Nest[ DivisorSigma[1, #] &, k, n]]][[1]] != Transpose[ FactorInteger[ k]][[1]], k += 2]; k]; (* Robert G. Wilson v, Aug 03 2017 *)

Crossrefs

Cf. A000203, A027598.

Sequence in context: A192355 A100251 A266607 * A020339 A351111 A154738

Adjacent sequences: A290048 A290049 A290050 * A290052 A290053 A290054

Keyword

nonn,more

Author

Altug Alkan, Aug 03 2017

Extensions

a(10)-a(23) from Giovanni Resta, Aug 03 2017

Status

approved