The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A309182 (1/3) times the number of n-member subsets of [3n] whose elements sum to a multiple of n. 2
 1, 2, 10, 42, 201, 1028, 5538, 30666, 173593, 1001402, 5864750, 34769364, 208267320, 1258574116, 7663720710, 46976034378, 289628805623, 1794932294978, 11175157356522, 69864075597442, 438403736549145, 2760351027094300, 17433869214973754, 110420300879752980 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also (1/2) times the number of n-member subsets of [3n-1] whose elements sum to a multiple of n. LINKS Alois P. Heinz, Table of n, a(n) for n = 1..1000 FORMULA a(n) = 1/(3n) * Sum_{d|n} binomial(3d,d)*(-1)^(n+d)*phi(n/d). MAPLE with(numtheory): a:= n-> add(binomial(3*d, d)*(-1)^(n+d)*         phi(n/d), d in divisors(n))/(3*n): seq(a(n), n=1..25); CROSSREFS Column k=3 of A309148. Sequence in context: A020988 A177238 A084480 * A099553 A119694 A286760 Adjacent sequences:  A309179 A309180 A309181 * A309183 A309184 A309185 KEYWORD nonn AUTHOR Alois P. Heinz, Jul 15 2019 STATUS approved

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

Last modified September 25 13:37 EDT 2021. Contains 347654 sequences. (Running on oeis4.)