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
Keywords
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
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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(d
Comments