This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A217768 #15 Mar 26 2013 02:31:08
%S A217768 34,53,23,19,26,41,31,38,49,52,68,82,112,80,103,76,110,123,4,83,101,
%T A217768 136,3,164,130,5,147,133,381,254,7,149,253,1,131,246,172,8,404,7,6,
%U A217768 312,148,209,309,241,487,328,9,260
%N A217768 Smallest number k > 0 for which sigma(k - n) = sigma(k + n).
%C A217768 The sigma() in the definition is the sum-of-divisors function A000203.
%C A217768 If m is negative, the definition uses the convention sigma(m) = sigma(-m).
%e A217768 a(4) = 19 because sigma(19 + 4) = sigma(23) = 1 + 23 = 24 and sigma(19 - 4) = sigma(15) = 1 + 3 + 5 + 15 = 24 and there is no k < 19 for which sigma(k + 4) = sigma(k - 4).
%e A217768 a(26) = 5 because sigma(5 + 26) = sigma(31) = 1 + 31 = 32 and sigma(5 - 26) = sigma(-21) = sigma(21) = 1 + 3 + 7 + 21 = 32.
%t A217768 Table[Min[Select[Range[500],DivisorSigma[1, # - n] == DivisorSigma[1, # + n] &]], {n,50}]
%Y A217768 Cf. A067135, A175876, A223091.
%K A217768 nonn
%O A217768 1,1
%A A217768 _Jayanta Basu_, Mar 24 2013