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A007012 a(n) is number of k for which C(n,k) is not divisible by n.
(Formerly M0248)
3

%I M0248

%S 1,0,2,2,3,2,5,2,5,4,5,2,8,2,9,8,9,2,9,2,11,8,9,2,15,6,9,10,15,2,20,2,

%T 17,8,5,10,15,2,9,10,19,2,23,2,19,20,17,2,29,8,17,20,19,2,29,10,24,8,

%U 17,2,35,2,33,18,33,16,19,2,11,20,27,2,33,2,9,30,19,16,41,2,31,28,9,2,32,16

%N a(n) is number of k for which C(n,k) is not divisible by n.

%C The number of nonzero terms in the polynomial (1+x)^n (mod n). Note that n is prime iff a(n)=2. - _T. D. Noe_, Feb 23 2006

%C For n > 0: a(n) = number of terms > 0 in n-th row of triangle A053200. - _Reinhard Zumkeller_, Jan 24 2014

%D J. H. Conway, personal communication.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H T. D. Noe, <a href="/A007012/b007012.txt">Table of n, a(n) for n = 0..1000</a>

%F a(n)=n+1-A020475(n) - _T. D. Noe_, Feb 23 2006

%t Prepend[ Array[ Length[ Select[ Table[ Binomial[ #, k ]/#, {k, 0, #} ], !IntegerQ[ # ]& ] ]&, 100 ], 1 ]

%o (Haskell)

%o a007012 n = a007012_list !! n

%o a007012_list = 1 : map (sum . map signum) (tail a053200_tabl)

%o -- _Reinhard Zumkeller_, Jan 24 2014

%K nonn

%O 0,3

%A _N. J. A. Sloane_.

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Last modified April 20 22:22 EDT 2019. Contains 322310 sequences. (Running on oeis4.)