A099985 a(n) = rad(2n), where rad = A007947.

2, 2, 6, 2, 10, 6, 14, 2, 6, 10, 22, 6, 26, 14, 30, 2, 34, 6, 38, 10, 42, 22, 46, 6, 10, 26, 6, 14, 58, 30, 62, 2, 66, 34, 70, 6, 74, 38, 78, 10, 82, 42, 86, 22, 30, 46, 94, 6, 14, 10, 102, 26, 106, 6, 110, 14, 114, 58, 118, 30, 122, 62, 42, 2, 130, 66, 134, 34, 138, 70, 142, 6

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

Cf. A007947, A065463, A099984, A204455.

Sequence in context: A266722 A343511 A232625 * A298299 A352597 A110765

Adjacent sequences: A099982 A099983 A099984 * A099986 A099987 A099988

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