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Date: 16-1-2020
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Date: 25-3-2020
604
Date: 20-7-2020
1864
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The idempotent numbers are given by
where is a Bell polynomial and is a binomial coefficient. A table of the first few is given below.
A000027 | A001788 | A036216 | A040075 | A050982 | A050988 | A050989 | |
1 | 1 | ||||||
2 | 2 | 1 | |||||
3 | 3 | 6 | 1 | ||||
4 | 4 | 24 | 12 | 1 | |||
5 | 5 | 80 | 90 | 20 | 1 | ||
6 | 6 | 240 | 540 | 240 | 30 | 1 | |
7 | 7 | 672 | 2835 | 2240 | 525 | 42 | 1 |
8 | 8 | 1792 | 13608 | 17920 | 7000 | 1008 | 56 |
9 | 9 | 4608 | 61236 | 129024 | 78750 | 18144 | 1764 |
10 | 10 | 11520 | 262440 | 860160 | 787500 | 272160 | 41160 |
REFERENCES:
Comtet, L. Advanced Combinatorics: The Art of Finite and Infinite Expansions, rev. enl. ed. Dordrecht, Netherlands: Reidel, p. 91, 1974.
Roman, S. The Umbral Calculus. New York: Academic Press, p. 85, 1984.
Sloane, N. J. A. Sequences A000027/M0472, A001788/M4161, A036216, A040075, A050982, A050988, and A050989 in "The On-Line Encyclopedia of Integer Sequences."
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