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%I #8 Apr 08 2019 18:58:51
%S 1,1,2,3,6,10,22,40,76,166,306,558,1260,2508,6876,13596,31068,66012,
%T 144636,298692,656532,1411650,3114050,6907892,12800744,24982760,
%U 51166280,112488680,239410280,501240080,1039913300,2346376556,4608703112,8900121992,18206157332
%N Sigmabonacci numbers: a(n)=a(n-1)+Sigma(a(n-2)). Sigma(n)=Sum of divisors of n.
%e a(9)=76=a(8)+Sigma(a(7))=40+(1+2+11+22)=40+36=76.
%t nxt[{a_,b_}]:={b,b+DivisorSigma[1,a]}; NestList[nxt,{1,1},40][[All,1]] (* _Harvey P. Dale_, Apr 08 2019 *)
%o (PARI) a(n) = if (n == 1, 1, if (n == 2, 1, a(n-1) + sigma(a(n-2)))); \\ _Michel Marcus_, Aug 15 2013
%K easy,nonn
%O 1,3
%A _Miklos Kristof_, Sep 24 2002
%E More terms from _Michel Marcus_, Aug 15 2013
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