OFFSET
1,2
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = n * A064989(n).
Sum_{n>=1} 1/a(n) = 2/Product_{k>=1} (1 - 1/(prime(k)*prime(k+1))) = 2.75321091... . - Amiram Eldar, Jan 07 2023
MATHEMATICA
a200746[n_Integer] := Block[{f, p, a},
f[x_] := Transpose@FactorInteger[x];
p[x_] := Which[
x == 1, 1,
x == 2, 2,
True, x NextPrime[x, -1]];
a[x_] := Times @@ Power[p /@ First[f[x]], Last[f[x]]];
a /@ Range[n]]; a200746[57] (* Michael De Vlieger, Dec 19 2014 *)
PROG
(PARI) a(n)=local(fm=factor(n)); prod(k=1, matsize(fm)[1], (fm[k, 1]*if(fm[k, 1]==2, 1, precprime(fm[k, 1]-1)))^fm[k, 2])
(Scheme, with memoization-macro definec) (definec (A200746 n) (if (<= n 2) n (* n (A064989 n)))) ;; Antti Karttunen, Dec 18 2014
CROSSREFS
KEYWORD
AUTHOR
Franklin T. Adams-Watters, Nov 25 2011
STATUS
approved