OFFSET
1,2
EXAMPLE
For n=9, A007947({C(9,k)}) = {1,3,6,42,42,42,42,6,3,1} includes 4 distinct values, thus generating 4 classes of k values: {0,9}, {1,8}, {2,7} and {3,4,5,6}. So a(9)=4.
MATHEMATICA
a[n_] = Length[ Union[ Table[ A007947[ binomial[ n, k ] ], {k, 0, n} ] ] ]
PROG
(PARI) a(n) = #Set(vector(ceil(n\2)+1, k, factorback(factorint(binomial(n, k-1))[, 1]))); \\ Michel Marcus, May 20 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved