A238330 Numbers n such that rad(sigma(n)) = 2*rad(n), where the "radical" of n, rad(n), is A007947 and sigma(n) is the sum of the divisors of n.

135, 891, 200655, 307125, 544635, 1672125, 2876211, 3138345, 4538625, 5016375, 5417685, 6517665, 11764935, 13179375, 13615875, 14705145, 15049125, 18309375, 40847625, 45623655, 84418425, 98041125, 99684375, 135442125, 153778905, 203870601, 262840851, 270571875

Offset

1,1

Comments

First 5 terms from MathOverflow.

Links

Donovan Johnson, Table of n, a(n) for n = 1..91 (terms < 10^11)

Sylvain Julien, MathOverflow: rad(sigma(n)) = 2*rad(n)

Mathematica

rad[n_] := Times @@ Transpose[FactorInteger[n]][[1]]; Select[Range[1000000], rad[DivisorSigma[1, #]] == 2*rad[#] &]

Prog

(PARI) rad(n)= my(p=factor(n)[, 1]); prod(i=1, length(p), p[i]);
isok(n) = rad(sigma(n)) == 2*rad(n); \\ Michel Marcus, Feb 28 2014

Crossrefs

Cf. A000203 (sigma), A007947 (rad).

Sequence in context: A211680 A212610 A336554 * A358002 A157734 A334128

Adjacent sequences: A238327 A238328 A238329 * A238331 A238332 A238333

Keyword

nonn

Author

T. D. Noe, Feb 27 2014

Extensions

More terms from Michel Marcus, Feb 28 2014

Status

approved