OFFSET
1,1
COMMENTS
Sigma(n) is the sum of the divisors of n: A000203.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..138 (terms < 10^13)
EXAMPLE
sigma(75) + sigma(76) = 124 + 140 = 264, and sigma(77) + sigma(78) = 96 + 168 = 264, so 75 is in the sequence.
MATHEMATICA
t = {}; s = DivisorSigma[1, Range[0, 3]]; n = 3; While[Length[t] < 10, n++; s = RotateLeft[s]; s[[4]] = DivisorSigma[1, n]; If[s[[1]] + s[[2]] == s[[3]] + s[[4]], AppendTo[t, n - 3]]]; t (* T. D. Noe, Jun 12 2013 *)
Module[{ds=DivisorSigma[1, Range[6*10^7]]}, Flatten[Position[Partition[ds, 4, 1], _?(Total[Take[#, 2]]==Total[Take[#, -2]]&), {1}, Heads->False]]] (* Harvey P. Dale, Sep 13 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Jun 11 2013
STATUS
approved