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URL: https://oeis.org/A286980

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A286980
Binomial coefficients binomial(n,k) = uv such that n>=2k and u > v, where gpf(u) < k, gpf(v) >= k (gpf(n)= is the greatest prime factor of n).
1
56, 126, 252, 792, 116280, 203490, 2035800, 573166440, 818809200, 2310789600, 8597496600, 1889912732400
OFFSET
1,1
COMMENTS
The corresponding pairs (n,k) are: (8,3), (9,4), (10,5), (12,5), (21,7), (21,8), (30,7), (33,13), (33,14), (36,13), (36,17), (56,13).
Subsequence of A286981.
LINKS
Earl F. Ecklund, Jr., Roger B. Eggleton, Paul Erdős and John L. Selfridge, On the prime factorization of binomial coefficients, Journal of the Australian Mathematical Society (Series A), Vol. 26, No. 3 (1978), pp. 257-269.
EXAMPLE
56 = Binomial(8,3) = 8*7, gpf(8) = 2 < 3 and gpf(7) = 7 >= 3, and 8 > 7, thus 56 is in the sequence.
CROSSREFS
Sequence in context: A157330 A038849 A003781 * A254463 A030443 A135803
KEYWORD
nonn,fini,full
AUTHOR
Amiram Eldar, May 17 2017
STATUS
approved