A126850 - OEIS

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A126850

a(n) = OrdinaryUnitarySigma(a(n-1)).

2, 3, 4, 7, 8, 15, 24, 60, 168, 480, 1512, 3360, 12096, 28448, 64512, 163760, 401760, 991872, 2399040, 6858000, 13999104, 32752000, 69400800, 172186560, 517867392, 1666990080, 5662137600, 14475575296, 33946612000, 73359820800, 158022774000

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OFFSET

2,1

LINKS

Table of n, a(n) for n=2..32.

FORMULA

a(n)= A107749(a(n-1)). - R. J. Mathar, Jun 15 2008

MAPLE

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

MATHEMATICA

f[2, e_] := 2^(e + 1) - 1;

f[p_, e_] := p^e + 1;

A107749[n_] := If[n == 1, 1, Times @@ f @@@ FactorInteger[n]];

a[n_] := a[n] = If[n == 2, 2, A107749[a[n - 1]]];

Table[a[n], {n, 2, 32}] (* Jean-François Alcover, Jul 22 2024, after Amiram Eldar in A107749 *)

CROSSREFS

Cf. A107749, A126849.

Cf. A107749, A126849, A007497.

Sequence in context: A092063 A227007 A370858 * A007497 A126882 A333801

Adjacent sequences: A126847 A126848 A126849 * A126851 A126852 A126853

KEYWORD

nonn

AUTHOR

Yasutoshi Kohmoto, Feb 24 2007

EXTENSIONS

Edited and extended by R. J. Mathar, Jun 15 2008

STATUS

approved