

A291138


a(n) is the smallest k such that psi(k) and phi(k) have same distinct prime factors when k is the product of n distinct primes (psi(k) = A001615(k) and phi(k) = A000010(k)), or 0 if no such k exists.


0




OFFSET

1,1


LINKS

Table of n, a(n) for n=1..10.


EXAMPLE

a(5) = 3570 = 2*3*5*7*17 because psi(3570) = 3*4*6*8*18 = 2^7*3^4, and phi(3570) = 2*4*6*16 = 2^8*3^1 and 3570 is the least number with 5 distinct prime factors having this property.


MATHEMATICA

Rest@ Values[#][[All, 1]] &@ KeySort@ PositionIndex@ Table[If[SameQ @@ #, PrimeNu@ n, 0] &@ Map[FactorInteger[#][[All, 1]] &, {EulerPhi@ n, n Sum[MoebiusMu[d]^2/d, {d, Divisors@ n}]}], {n, 10^6}] (* Michael De Vlieger, Aug 26 2017, after Michael Somos at A001615 *)


CROSSREFS

Cf. A000010 (phi), A005117 (squarefree), A001615 (psi), A007947 (radical).
Sequence in context: A055650 A000550 A124650 * A063903 A305009 A115005
Adjacent sequences: A291135 A291136 A291137 * A291139 A291140 A291141


KEYWORD

nonn,more


AUTHOR

Altug Alkan, Aug 18 2017


EXTENSIONS

a(10) from Giovanni Resta, Aug 26 2017


STATUS

approved



