OFFSET
1,1
COMMENTS
If we had a(1) = 1 (instead of 4), then this would be multiplicative and a permutation of the odd powerful numbers (A062739). - Amiram Eldar, Aug 11 2022
REFERENCES
From a puzzle proposed by Marc LeBrun.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = 2*zeta(2)*zeta(3)/(3*zeta(6)) - 3/4. - Amiram Eldar, Aug 11 2022
MATHEMATICA
a[1]=4; a[n_] := Thread[f = FactorInteger[n]; Times @@ Power[f[[All, 1]] // NextPrime , f[[All, 2]] + 1]]; Array[a, 50] (* Jean-François Alcover, Feb 03 2015 *)
PROG
(Haskell)
a045967 1 = 4
a045967 n = product $ zipWith (^)
(map a151800 $ a027748_row n) (map (+ 1) $ a124010_row n)
-- Reinhard Zumkeller, Jun 03 2013, Dec 23 2011
CROSSREFS
KEYWORD
easy,nonn,nice
AUTHOR
EXTENSIONS
More terms from David W. Wilson
STATUS
approved