A163666 Numbers k such that k=prime(sigma(phi(pi(k)))).

2, 5, 47, 107, 1613, 5653, 21557, 230047, 821603, 8145173, 47073007, 68939141, 76040521, 196388147, 240595631, 433046543, 1085166671, 2269551127, 4670405591, 9784786813, 104484802043, 420065905307, 474962067289, 2616252796471, 5804170333301, 11225933856497, 17730850486637, 43536271551811

Offset

1,1

Comments

It is obvious that all terms are primes.

Links

Table of n, a(n) for n=1..28.

Formula

a(n) = A000040(A018784(n)). - Max Alekseyev, Jun 25 2011

Mathematica

Do[If[n=Prime[m]; m==DivisorSigma[1, EulerPhi[PrimePi[n]]], Print[n]], {m, 235000000}]

Crossrefs

Cf. A000010, A000040, A000720, A000203, A163665.

Sequence in context: A023273 A041729 A078665 * A093552 A060808 A099658

Adjacent sequences: A163663 A163664 A163665 * A163667 A163668 A163669

Keyword

nonn

Author

Farideh Firoozbakht, Aug 04 2009

Extensions

a(20)-a(25) from Max Alekseyev, Jun 25 2011

a(26)-a(28) from Max Alekseyev, Jan 15 2026

Status

approved