This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A126850 #10 Jul 22 2024 06:06:40
%S A126850 2,3,4,7,8,15,24,60,168,480,1512,3360,12096,28448,64512,163760,401760,
%T A126850 991872,2399040,6858000,13999104,32752000,69400800,172186560,
%U A126850 517867392,1666990080,5662137600,14475575296,33946612000,73359820800,158022774000
%N A126850 a(n) = OrdinaryUnitarySigma(a(n-1)).
%F A126850 a(n)= A107749(a(n-1)). - _R. J. Mathar_, Jun 15 2008
%p A126850 A034448 := proc(n) local ifs,d ; if n = 1 then 1; else ifs := ifactors(n)[2] ; mul(1+ op(1,op(d,ifs))^op(2,op(d,ifs)),d=1..nops(ifs)) ; fi ; end: A006519 := proc(n) local i ; for i in ifactors(n)[2] do if op(1,i) = 2 then RETURN( op(1,i)^op(2,i) ) ; fi ; od: RETURN(1) ; end: A107749 := proc(n) local p2 ; p2 := A006519(n) ; numtheory[sigma](p2)*A034448(n/p2) ; end: A126850 := proc(n) option remember ; if n = 1 then 2; else A107749(A126850(n-1)) ; fi ; end: seq(A126850(n),n=1..40) ; # _R. J. Mathar_, Jun 15 2008
%t A126850 f[2, e_] := 2^(e + 1) - 1;
%t A126850 f[p_, e_] := p^e + 1;
%t A126850 A107749[n_] := If[n == 1, 1, Times @@ f @@@ FactorInteger[n]];
%t A126850 a[n_] := a[n] = If[n == 2, 2, A107749[a[n - 1]]];
%t A126850 Table[a[n], {n, 2, 32}] (* _Jean-François Alcover_, Jul 22 2024, after _Amiram Eldar_ in A107749 *)
%Y A126850 Cf. A107749, A126849.
%Y A126850 Cf. A107749, A126849, A007497.
%K A126850 nonn
%O A126850 2,1
%A A126850 _Yasutoshi Kohmoto_, Feb 24 2007
%E A126850 Edited and extended by _R. J. Mathar_, Jun 15 2008