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 A063972 a(n) is the smallest m such that usigma(m) = n (or 0 if no such m). 2
 1, 0, 2, 3, 4, 5, 0, 7, 8, 9, 0, 6, 0, 13, 0, 0, 16, 10, 0, 12, 0, 0, 0, 14, 0, 25, 0, 27, 0, 18, 0, 21, 32, 0, 0, 22, 0, 37, 0, 28, 0, 26, 0, 43, 0, 0, 0, 33, 0, 36, 0, 0, 0, 34, 0, 39, 0, 0, 0, 38, 0, 61, 0, 0, 64, 0, 0, 48, 0, 52, 0, 30, 0, 73, 0, 0, 0, 50, 0, 57, 0, 81, 0, 54, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS usigma(m) is the sum of unitary divisors of m, A034448. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 EXAMPLE a(12)=6 because the unitary divisors of 6 are 1,2,3,6; they sum to 12. MATHEMATICA usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); m = 100; v = Table[0, {m}];  Do[u = usigma[n]; If[u <= m && v[[u]] == 0, v[[u]] = n], {n, 1, m}]; v (* Amiram Eldar, Sep 22 2019 *) CROSSREFS Cf. A034444, A034448, A051444, A057637, A063973. Sequence in context: A267000 A224892 A265517 * A063973 A126441 A004181 Adjacent sequences:  A063969 A063970 A063971 * A063973 A063974 A063975 KEYWORD nonn AUTHOR Labos Elemer, Sep 05 2001 EXTENSIONS Edited by Don Reble, May 14 2006 STATUS approved

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Last modified April 21 13:04 EDT 2021. Contains 343153 sequences. (Running on oeis4.)