A050399 Least k such that n = A009195(k) (= gcd(phi(k), k)).

1, 4, 9, 8, 25, 18, 49, 16, 27, 50, 121, 36, 169, 98, 225, 32, 289, 54, 361, 100, 147, 242, 529, 72, 125, 338, 81, 196, 841, 450, 961, 64, 1089, 578, 1225, 108, 1369, 722, 507, 200, 1681, 294, 1849, 484, 675, 1058, 2209, 144, 343, 250, 2601, 676, 2809

Offset: 1

Author

Christian G. Bower, Nov 15 1999

Keywords

• nonn

Comments

Coincides with A072995 for many terms, but differs, e.g., in n = 20, 40, 52, ... in addition to the zeros in A072995. See also the comments in A072994. - M. F. Hasler, Feb 23 2014

a(n) <= n^2. - Robert G. Wilson v, Feb 27 2014

Links

• Robert G. Wilson v, Table of n, a(n) for n = 1..10000

Programs

Mathematica

t = Table[0, {10000}]; k = 1; While[k < 100000001, a = GCD[k, EulerPhi@ k]; If[a < 10001 && t[[a]] == 0, t[[a]] = k; Print[{a, k}]]; k++]; t (* Robert G. Wilson v, Feb 27 2014 *)

PARI

A050399=n->for(k=1,oo,gcd(eulerphi(k),k)==n&&return(k)) \\ M. F. Hasler, Feb 23 2014