A069143 a(1) = a(2) = 1; a(n) = sigma(a(n-1)+a(n-2)).

1, 1, 3, 7, 18, 31, 57, 180, 320, 1092, 2478, 10368, 25704, 100800, 393120, 1965600, 10326624, 39657600, 131580288, 511223790, 1469266560, 4911616440, 22120488000, 95841111600, 460020244320, 2163425531904, 9805180170240

Offset

1,3

Links

Robert Israel, Table of n, a(n) for n = 1..138

Maple

f:= proc(n) option remember; numtheory:-sigma(procname(n-1)+procname(n-2)) end proc:
f(1):= 1: f(2):= 1:
seq(f(n), n=1..40); # Robert Israel, Mar 05 2025

Mathematica

a[1] = a[2] = 1; a[n_] := a[n] = DivisorSigma[1, a[n - 1] + a[n - 2]]; Table[a[n], {n, 27}]
RecurrenceTable[{a[1]==a[2]==1, a[n]==DivisorSigma[1, a[n-1]+a[n-2]]}, a, {n, 30}] (* Harvey P. Dale, Feb 15 2015 *)

Crossrefs

Sequence in context: A331713 A348391 A327321 * A097007 A308445 A328653

Adjacent sequences: A069140 A069141 A069142 * A069144 A069145 A069146

Keyword

nonn,changed

Author

Joseph L. Pe, Apr 08 2002

Extensions

Edited and extended by Robert G. Wilson v, Apr 11 2002

Status

approved