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%I #27 Jul 26 2016 22:12:15
%S 14,7,319,341,537
%N Least k such that sigma(k*n) = sigma(k*n+1), or 0 if no such k exists.
%C Terms 6 through 30, with 0 signifying no such k <= 10^6: {0, 2, 220708, 1649, 23039, 87, 0, 6141, 1, 179, 110354, 873, 0, 86, 0, 5813, 62, 58, 0, 37497, 17149, 699, 0, 33, 0}. - _Michael De Vlieger_, Jul 25 2016
%C a(28) = 16806458, from A002961 b-file. - _Michel Marcus_, Jul 26 2016
%C If a(n) = 0, then a(m*n) = 0 for all m > 0. If c is a divisor of a(n), then a(c*n) = a(n)/c. - _Chai Wah Wu_, Jul 26 2016
%H Michel Marcus, <a href="/A275337/a275337.txt">Some terms</a>
%e a(3) = 319 because sigma(319*3) = sigma(319*3+1) = 1440.
%t Table[SelectFirst[Range[10^6], DivisorSigma[1, # n] == DivisorSigma[1, # n + 1] &], {n, 30}] /. k_ /; MissingQ@ k -> 0 (* _Michael De Vlieger_, Jul 25 2016, Version 10.2 *)
%o (PARI) a(n) = {my(k = 1); while (sigma(k*n) != sigma(k*n+1), k++); k;} \\ _Michel Marcus_, Jul 26 2016
%Y Cf. A002961.
%K nonn,more
%O 1,1
%A _Altug Alkan_, Jul 24 2016
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