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 A023898 Divisor balance of n is an integer. 5
 1, 2, 4, 8, 9, 16, 18, 32, 36, 45, 64, 72, 81, 90, 98, 126, 128, 144, 162, 180, 225, 234, 256, 288, 294, 324, 360, 363, 396, 450, 484, 512, 539, 576, 625, 648, 720, 726, 729, 784, 882, 900, 1008, 1024, 1078, 1125, 1152, 1250, 1296, 1440, 1452, 1458, 1800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA Divisor balance of n = sum_{d divides n} {d / phi(d)} where phi is Euler's phi function. EXAMPLE 45 is in this list because its divisors are 1,3,5,9,15 and 45, the corresponding fractions are : (1, 3/2, 5/4, 3/2, 15/8, 15/8) and their sum is 9, which is an integer. MATHEMATICA Select[ Range[ 2000 ], Function[ n, IntegerQ[ Plus @@ Map[ #/EulerPhi[ # ]&, Divisors[ n ] ] ] ] ] dbiQ[n_]:=Module[{d=Divisors[n]}, IntegerQ[Total[d/EulerPhi[d]]]]; Select[ Range[ 2000], dbiQ] (* Harvey P. Dale, Jul 25 2016 *) CROSSREFS Cf. A023899 (corresponding values of the divisor balance). Cf. A239886, A239887 for a version with proper divisors. Sequence in context: A114400 A341742 A330710 * A125853 A080025 A152111 Adjacent sequences:  A023895 A023896 A023897 * A023899 A023900 A023901 KEYWORD nonn AUTHOR STATUS approved

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Last modified April 14 05:41 EDT 2021. Contains 342946 sequences. (Running on oeis4.)