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 A241474 Smallest k such that tau(k)=reversal(k-n). 0
 3, 6, 5, 8, 7, 9, 407, 68, 11, 14, 13, 18, 413, 20, 17, 24, 19, 22, 49, 21020, 23, 25, 27, 104, 65, 32, 29, 628, 31, 34, 35, 40, 53, 38, 37, 6136, 77, 44, 41, 2140, 43, 46, 4043, 50, 47, 49, 51, 56, 40049, 130, 53, 652, 57, 58, 95, 116, 59, 62, 61, 480, 65, 68 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS tau(n) = A000005(n) is the number of divisors of n. Observation : The sequence shows pairs of the form (m, m +/- 1) such as: (6,5), (8,7), (14,13), (34,35), (38,37), (57,58), (62,61), (74,73), (93,94), (94,95), (104,105), (118,119), (135,136), (142,143), (177,178), (188,187), (244,245), ... LINKS EXAMPLE a(20)=21020 because tau(21020) = 12 = reversal(21) = reversal(21020-20). MATHEMATICA Table[k=n+1; While[!(k>n)||!DivisorSigma[0, k]==FromDigits[Reverse[IntegerDigits[k-n]]], k++]; k, {n, 80}] PROG (PARI) rev(n) = subst(Polrev(digits(n)), x, 10); a(n) = {k = n+1; while (numdiv(k) != rev(k-n), k++); k; } \\ Michel Marcus, Apr 23 2014 CROSSREFS Cf. A000005, A004086. Sequence in context: A201418 A123688 A082284 * A259556 A063520 A078677 Adjacent sequences:  A241471 A241472 A241473 * A241475 A241476 A241477 KEYWORD nonn,base AUTHOR Michel Lagneau, Apr 23 2014 STATUS approved

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Last modified October 22 07:48 EDT 2019. Contains 328315 sequences. (Running on oeis4.)