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 A000458 a(0) = a(1) = 1; thereafter a(n) = sigma(a(n-1)) + sigma(a(n-2)). 1
 1, 1, 2, 4, 10, 25, 49, 88, 237, 500, 1412, 3570, 12846, 36072, 126504, 493920, 2358720, 12292224, 49984224, 171237888, 642804078, 1980490350, 6380883000, 27032104440, 117961599600, 555861355920, 2623445776224 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS T. D. Noe, Table of n, a(n) for n=0..100 MAPLE A000458 := proc(n) options remember; if n <= 1 then RETURN(1) else sigma(A000458(n-1))+sigma(A000458(n-2)); fi; end; MATHEMATICA a[0] = a[1] = 1; a[n_] := a[n] = DivisorSigma[1, a[n-1]] + DivisorSigma[1, a[n-2]]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Feb 08 2016 *) CROSSREFS Sequence in context: A148090 A148091 A123420 * A089928 A173610 A036887 Adjacent sequences:  A000455 A000456 A000457 * A000459 A000460 A000461 KEYWORD nonn AUTHOR STATUS approved

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