cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A292880 Number of sequences of balls colored with at most n colors such that exactly three balls are of a color seen earlier in the sequence.

Original entry on oeis.org

1, 32, 633, 10744, 173705, 2798376, 45930577, 777101648, 13638044529, 249079033360, 4741200949001, 94104123729672, 1947270419971513, 41985753920469464, 942531024150018465, 22009425078894009376, 534085741053864862817, 13454221423402868473728, 351483652960252663137049, 9512821482149972773978520
Offset: 1

Views

Author

Jeremy Dover, Sep 25 2017

Keywords

Comments

Note that any such sequence has at least 4 balls and at most n+3.

Crossrefs

Row sums of triangle A292879.

Formula

a(n) = n! * Sum_{k=4..n+3} [binomial(k,4)+10*binomial(k,5)+15*binomial(k,6)]/(n+3-k)!
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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