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A225493
Numbers having only strong prime factors, cf. A051634.
5
1, 11, 17, 29, 37, 41, 59, 67, 71, 79, 97, 101, 107, 121, 127, 137, 149, 163, 179, 187, 191, 197, 223, 227, 239, 251, 269, 277, 281, 289, 307, 311, 319, 331, 347, 367, 379, 397, 407, 419, 431, 439, 451, 457, 461, 479, 487, 493, 499, 521, 541, 557, 569, 587
OFFSET
1,2
LINKS
FORMULA
Multiplicative closure of A051634.
PROG
(Haskell)
import Data.Set (singleton, fromList, union, deleteFindMin)
a225493 n = a225493_list !! (n-1)
a225493_list = 1 : h (singleton p) ps [p] where
(p:ps) = a051634_list
h s xs'@(x:xs) ys
| m > x = h (s `union` (fromList $ map (* x) (1 : ys))) xs ys
| otherwise = m : h (s' `union` (fromList $ map (* m) ys')) xs' ys'
where ys' = m : ys; (m, s') = deleteFindMin s
CROSSREFS
Cf. A225494 (balanced), A225495 (weak), A225496 (non-balanced).
Sequence in context: A110055 A240095 A105886 * A051634 A038918 A220293
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 09 2013
STATUS
approved