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%I #12 Apr 18 2021 05:44:13
%S 1,5,25,120,580,2800,13500,65100,313940,1513820,7299760,35200020,
%T 169736780,818482260,3946776920,19031623000
%N Number of quinternary cubefree words of length n.
%o (Python)
%o from itertools import product
%o def cf(s):
%o for l in range(1, len(s)//3 + 1):
%o for i in range(len(s) - 3*l + 1):
%o if s[i:i+l]*2 == s[i+l:i+3*l]: return False
%o return True
%o def a(n):
%o if n == 0: return 1
%o return 5*sum(cf("0"+"".join(w)) for w in product("01234", repeat=n-1))
%o print([a(n) for n in range(0, 10)]) # _Michael S. Branicky_, Apr 16 2021
%Y Cf. A028445, A051042, A051043.
%K more,nonn
%O 0,2
%A _Sascha Kurz_, Mar 22 2002
%E a(0) prepended and a(14)-a(15) by _Michael S. Branicky_, Apr 16 2021
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