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a(n) = rad(2n), where rad = A007947.
5

%I #24 Nov 19 2022 04:45:48

%S 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,

%T 14,58,30,62,2,66,34,70,6,74,38,78,10,82,42,86,22,30,46,94,6,14,10,

%U 102,26,106,6,110,14,114,58,118,30,122,62,42,2,130,66,134,34,138,70,142,6

%N a(n) = rad(2n), where rad = A007947.

%C Bisection of A007947.

%H Antti Karttunen, <a href="/A099985/b099985.txt">Table of n, a(n) for n = 1..20000</a>

%F a(n) = 2 * A204455(n).

%F a(n) = A007947(2n). - _Wesley Ivan Hurt_, May 07 2022

%F 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

%p 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

%t Table[Product[p, {p, Select[Divisors[2 n], PrimeQ]}], {n, 100}] (* _Wesley Ivan Hurt_, May 08 2022 *)

%t a[n_] := Times @@ (First /@ FactorInteger[2*n]); Array[a, 100] (* _Amiram Eldar_, Nov 19 2022 *)

%o (PARI) A099985(n) = factorback(factorint(n+n)[, 1]); \\ _Antti Karttunen_, May 08 2022

%Y Cf. A007947, A065463, A099984, A204455.

%K nonn,easy

%O 1,1

%A _N. J. A. Sloane_, Nov 19 2004

%E More terms from _Emeric Deutsch_, Dec 15 2004

%E Name changed by _Wesley Ivan Hurt_, May 07 2022