A110192 Least k > n such that phi(k) = 2*phi(n), where phi is Euler's totient function.

3, 3, 5, 5, 15, 8, 13, 15, 13, 15, 25, 15, 35, 21, 17, 17, 51, 21, 37, 32, 35, 25, 69, 32, 41, 35, 37, 35, 87, 32, 61, 51, 41, 51, 65, 39, 73, 57, 65, 51, 123, 45, 129, 55, 65, 69, 141, 51, 129, 55, 85, 65, 159, 57, 123, 65, 73, 87, 177, 64, 143, 77, 73, 85, 97, 75, 161, 85

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Formula

a(n) = A110179(n) + n.

Mathematica

Table[k=n+1; e=EulerPhi[n]; While[EulerPhi[k] != 2e, k++ ]; k, {n, 100}]

Prog

(PARI) a(n) = vecmin(select(x -> x > n, invphi(2*eulerphi(n)))); \\ Amiram Eldar, Nov 05 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000010, A110179.

Sequence in context: A325679 A147198 A147048 * A014414 A087745 A087756

Adjacent sequences: A110189 A110190 A110191 * A110193 A110194 A110195

Keyword

nonn,look,changed

Author

T. D. Noe, Jul 15 2005

Status

approved