OFFSET
1,4
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
Krassimir Atanassov, New integer functions, related to φ and σ functions, Bull. Number Theory Related Topics, Vol. 11, No. 1 (1987), pp. 3-26.
G. L. Cohen, D. E. Iannucci, Derived Sequences, J. Int. Seq. 6 (2003) #03.1.1
Vaclav Kotesovec, Graph - the asymptotic ratio (500000000 terms).
J. Sandor, B. Crstici, Handbook of Number Theory II, Kluwer, 2004, page 337.
FORMULA
a(n)=1 for all squarefree n.
Dirichlet g.f.: zeta^2(s-1)*product_{primes p} (1-2*p^(1-s)+p^(2-2s)+p^(-s)). - R. J. Mathar, Jan 19 2012
MAPLE
A203639 := proc(n)
local a, f, e ;
a :=1;
for f in ifactors(n)[2] do
e := op(2, f) ;
p := op(1, f) ;
a := a*e*p^(e-1) ;
end do;
a;
end proc; # R. J. Mathar, Jan 11 2012
MATHEMATICA
Table[n*Times @@ Transpose[FactorInteger[n]][[2]] / Last[Select[Divisors[n], SquareFreeQ]], {n, 1, 100}] (* Vaclav Kotesovec, Dec 18 2019 *)
f[p_, e_] := e*p^(e-1); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 21 2020 *)
PROG
(PARI) a(n)=my(f=factor(n)); n*prod(i=1, #f~, f[i, 2]/f[i, 1]) \\ Charles R Greathouse IV, Dec 09 2016
(PARI) for(n=1, 100, print1(direuler(p=2, n, (1 + X/(1 - p*X)^2))[n], ", ")) \\ Vaclav Kotesovec, Jun 14 2020
(Scheme, with memoization-macro definec)
(definec (A203639 n) (if (= 1 n) n (* (A067029 n) (expt (A020639 n) (+ -1 (A067029 n))) (A203639 (A028234 n)))))
;; Antti Karttunen, Sep 13 2017
CROSSREFS
KEYWORD
nonn,mult,easy
AUTHOR
R. J. Mathar, Jan 04 2012
EXTENSIONS
Terms a(1)-a(24) confirmed and terms a(25)-a(100) added by John W. Layman, Jan 04 2012
STATUS
approved