A359182 Totient of numbers of least prime signature: a(n) = A000010(A025487(n)).

1, 1, 2, 2, 4, 4, 8, 8, 8, 16, 12, 16, 16, 32, 24, 32, 32, 64, 48, 48, 64, 48, 72, 64, 128, 96, 96, 128, 96, 144, 128, 256, 192, 192, 256, 192, 288, 240, 256, 512, 288, 384, 288, 432, 384, 512, 384, 576, 480, 512, 1024, 576, 768, 480, 576, 864, 768, 1024, 768

Offset: 1

Author

Hal M. Switkay, Dec 18 2022

Keywords

• nonn

Comments

This sequence is to A146288 as phi (A000010, the totient function) is to tau (A000005, the number of divisors function).

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 1..10000 (terms 1..160 from Hal M. Switkay)

Crossrefs

Cf. A000005, A000010, A025487, A146288.

Programs

Mathematica

s = {1}; Do[If[GreaterEqual @@ (f = FactorInteger[n])[[;; , 2]] && PrimePi[f[[-1, 1]]] == Length[f], AppendTo[s, EulerPhi[n]]], {n, 2, 3500}]; s (* Amiram Eldar, Dec 19 2022 *)

PARI

is(n) = {if(n==1, return(1)); my(f = factor(n));  f[#f~, 1] == prime(#f~) && vecsort(f[, 2], , 4) == f[, 2]}; \\ A025487
lista(nn) = apply(eulerphi, select(is, [1..nn])); \\ Michel Marcus, Dec 19 2022