The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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. 0
 1, 32, 633, 10744, 173705, 2798376, 45930577, 777101648, 13638044529, 249079033360, 4741200949001, 94104123729672, 1947270419971513, 41985753920469464, 942531024150018465, 22009425078894009376, 534085741053864862817, 13454221423402868473728, 351483652960252663137049, 9512821482149972773978520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Note that any such sequence has at least 4 balls and at most n+3. LINKS Table of n, a(n) for n=1..20. FORMULA a(n) = n! * Sum_{k=4..n+3} [binomial(k,4)+10*binomial(k,5)+15*binomial(k,6)]/(n+3-k)! CROSSREFS Row sums of triangle A292879. Sequence in context: A013699 A283279 A004337 * A255262 A181240 A140802 Adjacent sequences: A292877 A292878 A292879 * A292881 A292882 A292883 KEYWORD nonn AUTHOR Jeremy Dover, Sep 25 2017 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 27 05:14 EDT 2023. Contains 365674 sequences. (Running on oeis4.)