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 A292558 a(n) is the smallest number k such that sigma(k) - 2k = 2^n. 0
 20, 12, 56, 550, 572, 108, 860, 952, 1232, 6328, 3708, 40540, 37072, 79288, 327260, 357112, 302000, 527296, 1764056, 6506512, 38559776, 21893248, 42257216, 167771740, 90798560, 469761208, 508198064, 490304800, 1353048560, 2951488480, 5067417200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n > 31, a(n) > 1.724 * 10^10. LINKS EXAMPLE sigma(20) - 2*20 = 2^1, a(1) = 20. sigma(108) - 2*108 = 64 = 2^6, a(6) = 108. MATHEMATICA Table[k = 1; While[Log[2, DivisorSigma[1, k] - 2k] != n, k++]; k, {n, 30}] PROG (PARI) a(n) = my(k=1); while(sigma(k) - 2*k != 2^n, k++); k; \\ Michel Marcus, Sep 19 2017 CROSSREFS Cf. A033880, A088831, A088832, A088833, A141547, A175989, A275996. Sequence in context: A154043 A073868 A215028 * A040382 A223283 A076119 Adjacent sequences:  A292555 A292556 A292557 * A292559 A292560 A292561 KEYWORD nonn AUTHOR XU Pingya, Sep 19 2017 STATUS approved

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Last modified January 17 05:26 EST 2019. Contains 319207 sequences. (Running on oeis4.)