A072993 Numbers n such that phi(n) divides C(2n,n).

1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 15, 18, 21, 22, 26, 29, 30, 33, 35, 41, 42, 43, 44, 45, 52, 56, 60, 66, 67, 69, 70, 73, 74, 75, 76, 77, 78, 82, 86, 87, 88, 89, 92, 95, 99, 100, 105, 106, 110, 115, 116, 119, 122, 123, 124, 126, 127, 129, 133, 135, 138, 142, 143, 146

Offset

1,2

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..10000

Vaclav Kotesovec, Plot of a(n)/n for n = 1..60000

Formula

It seems that a(n) is asymptotic to C*n with C=2.3...

Mathematica

Select[Range[200], Divisible[Binomial[2*#, #], EulerPhi[#]] &] (* Vaclav Kotesovec, Feb 15 2019 *)

Prog

(PARI) isok(n) = ! (binomial(2*n, n) % eulerphi(n)); \\ Michel Marcus, Nov 28 2013

Crossrefs

Sequence in context: A307625 A165722 A082400 * A018444 A032378 A342726

Adjacent sequences: A072990 A072991 A072992 * A072994 A072995 A072996

Keyword

easy,nonn

Author

Benoit Cloitre, Aug 21 2002

Status

approved