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 A051444 Smallest k such that sigma(k) = n, or 0 if there is no such k, where sigma(i) = A000203(i) = sum of divisors of i. 15
 1, 0, 2, 3, 0, 5, 4, 7, 0, 0, 0, 6, 9, 13, 8, 0, 0, 10, 0, 19, 0, 0, 0, 14, 0, 0, 0, 12, 0, 29, 16, 21, 0, 0, 0, 22, 0, 37, 18, 27, 0, 20, 0, 43, 0, 0, 0, 33, 0, 0, 0, 0, 0, 34, 0, 28, 49, 0, 0, 24, 0, 61, 32, 0, 0, 0, 0, 67, 0, 0, 0, 30, 0, 73, 0, 0, 0, 45, 0, 57, 0, 0, 0, 44, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 REFERENCES R. K. Guy, Unsolved Problems Theory of Numbers, B1. LINKS T. D. Noe, Table of n, a(n) for n=1..10000 EXAMPLE sigma(4)=7, 4 is the smallest, so a(7)=4. MATHEMATICA Do[ k = 1; While[ DivisorSigma[ 1, k ] != n && k < 10^4, k++ ]; If[ k != 10^4, Print[ k ], Print[ 0 ] ], {n, 1, 100} ] CROSSREFS Cf. A002192, A000203, A007626. Sequence in context: A080367 A066913 A090303 * A057637 A167485 A140508 Adjacent sequences:  A051441 A051442 A051443 * A051445 A051446 A051447 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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