A211777 Numbers n such that Sum_{d_A000010(x).

2, 3, 5, 7, 8, 11, 12, 13, 17, 19, 23, 29, 31, 32, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 80, 81, 83, 89, 97, 101, 103, 107, 109, 113, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 189, 191, 193, 196, 197, 199, 211, 223, 227, 229, 233

Offset: 1

Author

Jaroslav Krizek, Apr 20 2012

Keywords

• nonn

Comments

Union primes (A000040) and A211778.

Examples

			For n = 32 holds: 1/1 + 1/2 + 2/4 + 4/8 + 8/16 = 3 (integer).
		

Crossrefs

Cf: A066862 (numbers n such that Sum_{d | n} phi(d) / d is an integer).

Programs

Mathematica

t = {}; Do[d2 = Sum[EulerPhi[d]/d, {d, Most[Divisors[n]]}]; If[IntegerQ[d2], AppendTo[t, n]], {n, 2, 233}]; t (* T. D. Noe, Apr 26 2012 *)

PARI

is(n)=denominator(sumdiv(n,d,if(dCharles R Greathouse IV, Feb 21 2013