OFFSET
1,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1038 terms from T. D. Noe)
Daniel Mondot, Table of n, a(n) for n = 1..10000 with factorizations
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p prime} (1 + 1/p^p) = 1.2967126856... - Amiram Eldar, Oct 13 2020
EXAMPLE
3^3*5^5 = 84375.
PROG
(Haskell)
import Data.Set (empty, fromList, deleteFindMin, union)
import qualified Data.Set as Set (null, map)
a048102 n = a048102_list !! (n-1)
a048102_list = 1 : f empty [1] a051674_list where
f s ys pps'@(pp:pps)
| Set.null s = f (fromList (map (* pp) ys)) (pp:ys) pps
| pp < m = f (s `union` Set.map (* pp) s `union`
fromList (map (* pp) ys)) ys pps
| otherwise = m : f s' (m:ys) pps'
where (m, s') = deleteFindMin s
-- Reinhard Zumkeller, Jan 21 2012
(PARI) isok(n) = my(f = factor(n)); for (k=1, #f~, if (f[k, 1] != f[k, 2], return(0))); 1; \\ Michel Marcus, Apr 29 2016
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
EXTENSIONS
More terms from Naohiro Nomoto, Jun 28 2001
STATUS
approved