OFFSET
1,1
COMMENTS
Bisection of A007947.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..20000
FORMULA
a(n) = 2 * A204455(n).
a(n) = A007947(2n). - Wesley Ivan Hurt, May 07 2022
Sum_{k=1..n} a(k) ~ c * n^2, where c = (4/5) * Product_{p prime} (1 - 1/(p*(p+1))) = (4/5) * A065463 = 0.563553... . - Amiram Eldar, Nov 19 2022
MAPLE
with(numtheory): A007947 := proc(n) local i, t1, t2; t1 :=ifactors(n)[2]; t2 := mul(t1[i][1], i=1..nops(t1)); end: seq(A007947(2*n), n=1..78); # Emeric Deutsch, Dec 15 2004
MATHEMATICA
Table[Product[p, {p, Select[Divisors[2 n], PrimeQ]}], {n, 100}] (* Wesley Ivan Hurt, May 08 2022 *)
a[n_] := Times @@ (First /@ FactorInteger[2*n]); Array[a, 100] (* Amiram Eldar, Nov 19 2022 *)
PROG
(PARI) A099985(n) = factorback(factorint(n+n)[, 1]); \\ Antti Karttunen, May 08 2022
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 19 2004
EXTENSIONS
More terms from Emeric Deutsch, Dec 15 2004
Name changed by Wesley Ivan Hurt, May 07 2022
STATUS
approved