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A048686
Number of classes generated by function A007947 when applied to binomial coefficients.
0
1, 2, 2, 3, 3, 4, 4, 4, 4, 6, 6, 6, 7, 8, 8, 9, 8, 10, 8, 10, 11, 12, 12, 12, 13, 12, 12, 15, 15, 16, 14, 14, 14, 15, 16, 19, 18, 18, 18, 21, 19, 22, 21, 22, 23, 24, 24, 24, 22, 24, 25, 27, 23, 25, 24, 25, 29, 29, 28, 31, 31, 32, 30, 28, 29, 33, 31, 32, 34, 36, 35, 37, 36, 35, 36
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
Sequence in context: A074794 A234309 A306921 * A278959 A377108 A090501
KEYWORD
nonn
AUTHOR
STATUS
approved