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 A211777 Numbers n such that Sum_{d_
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Union primes (A000040) and A211778. LINKS EXAMPLE For n = 32 holds: 1/1 + 1/2 + 2/4 + 4/8 + 8/16 = 3 (integer). MAPLE with(numtheory); A211777:= proc(q) local b, d, j, n; for n from 2 to q do   b:=divisors(n); d:=add(phi(b[j])/b[j], j=1..nops(b))-phi(n)/n;   if trunc(d)=d then print(n); fi; od; end: A211777(10000); # Paolo P. Lava, Feb 01 2013 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 *) PROG (PARI) is(n)=denominator(sumdiv(n, d, if(d

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Last modified May 26 08:39 EDT 2020. Contains 334620 sequences. (Running on oeis4.)