A196748 Numbers n such that 3 and 5 do not divide swing(n) = A056040(n).
0, 1, 2, 20, 24, 54, 60, 61, 62, 72, 73, 74, 504, 510, 511, 512, 560, 564, 1512, 1513, 1514, 1520, 1620, 1621, 1622, 6320, 6324, 6372, 6373, 6374, 6500, 6504, 6552, 6553, 6554, 6560, 13122, 13123, 13124, 13770, 13771, 13772, 13824, 13850, 15072, 15073, 15074
Offset: 1
Keywords
Links
- Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
- P. Erdos, R. L. Graham, I. Z. Russa and E. G. Straus, On the prime factors of C(2n,n), Math. Comp. 29 (1975), 83-92.
- Peter Luschny, On the prime factors of the swinging factorial.
Programs
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Maple
# The function Search is defined in A196747. A196748_list := n -> Search(n,[3,5]): # n is a search limit
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Mathematica
(* A naive solution *) sf[n_] := n!/Quotient[n, 2]!^2; Select[Range[0, 16000], !Divisible[sf[#], 3] && !Divisible[sf[#], 5] &] (* Jean-François Alcover, Jun 28 2013 *)
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PARI
valp(n,p)=my(s); while(n\=p, s+=n); s is(n)=valp(n,3)==2*valp(n\2,3) && valp(n,5)==2*valp(n\2,5) \\ Charles R Greathouse IV, Feb 02 2016
Comments