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 A294347 a(n) is the smallest number whose deficiency or abundance is equal to n, or a(n) = 0 if such a number does not exist. 3
 6, 1, 3, 18, 5, 9, 7, 50, 22 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS If nonzero, a(9) > 10^9. - Michel Marcus, Oct 29 2017 From Robert Israel, Oct 29 2017: (Start) If n is odd, then a(n) must be a square or twice a square (A028982). If nonzero, a(9) > 10^13. Some other values: a(11)=244036, a(17)=100, a(19)=25, a(25)=98, a(31)=15376, a(37)=484, a(39)=162, a(41)=49, a(47)=225, a(51)=72. (End) a(n) > 10^20 for n in (9, 13, 15, 21, 23, 27, 29, 33, 35, 43, 45); see the intersection of A234285 and A234286. - Michel Marcus, Oct 30 2017 For the intersection mentioned above see A294406. - Omar E. Pol, Nov 01 2017 LINKS Nichole Davis, Dominic Klyve and Nicole Kraght, On the difference between an integer and the sum of its proper divisors, Involve, Vol. 6 (2013), No. 4, 493-504; DOI: 10.2140/involve.2013.6.493. Raven Dean, Rick Erdman, Dominic Klyve, Emily Lycette, Melissa Pidde, and Derek Wheel, Families of Values of the Excedent Function sigma(n)-2n, Missouri J. Math. Sci., Volume 27, Issue 1 (2015), 37-46. MATHEMATICA Table[k = 1; While[Abs[2 k - DivisorSigma[1, k]] != n, k++]; k, {n, 0, 8}] (* Michael De Vlieger, Oct 30 2017 *) PROG (PARI) a(n) = {my(k=1); while (abs(2*k-sigma(k)) != n, k++); k; } \\ Michel Marcus, Oct 29 2017 CROSSREFS Cf. A000203, A000396, A005100, A005101, A028982, A033879, A033880, A234285, A234286, A294386, A294393, A294406. Sequence in context: A176399 A273081 A181552 * A229606 A101023 A195303 Adjacent sequences:  A294344 A294345 A294346 * A294348 A294349 A294350 KEYWORD nonn,more,hard AUTHOR Omar E. Pol, Oct 29 2017 STATUS approved

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Last modified July 28 19:33 EDT 2021. Contains 346335 sequences. (Running on oeis4.)