A173146 sigma(phi(n)) = rad(n), where phi(n)= Euler totient function, sigma(n)= sum of divisors of n, rad(n)= product of primes that divide n.

3, 15, 255, 2418, 65535, 110771178, 4294967295

Offset

1,1

Links

Table of n, a(n) for n=1..7.

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972

Example

Phi(3) = 2, sigma(2) = 3 and rad(3) = 3 Phi(15) = 8, sigma(8) = 15, and rad(15) = 15 3 = 3, 15 = 3.5, 255 = 3.5.17, 2418 = 2.3.13.31, 65535 = 3.5.17.257, 110771178 = 2.3.7.19.127.1093, 4294967295 = 3.5.17.257.65537

Maple

with(numtheory): for n from 1 to 5000000000 do : t1 := ifactors(n)[2] : t2 := mul(t1[i][1], i=1..nops(t1)): if sigma(phi(n)) = t2 then print (n): else fi : od :

Crossrefs

Cf. A000010, A000203, A007947.

Sequence in context: A288986 A288988 A257018 * A139289 A116518 A247174

Adjacent sequences: A173143 A173144 A173145 * A173147 A173148 A173149

Keyword

nonn

Author

Michel Lagneau, Feb 11 2010

Status

approved