A026817 Number of sets which can be obtained by selecting unique elements from two sets with 2n and 3n elements respectively and n common elements.

6, 23, 51, 90, 140, 201, 273, 356, 450, 555, 671, 798, 936, 1085, 1245, 1416, 1598, 1791, 1995, 2210, 2436, 2673, 2921, 3180, 3450, 3731, 4023, 4326, 4640, 4965, 5301, 5648, 6006, 6375, 6755, 7146, 7548, 7961, 8385, 8820, 9266, 9723, 10191, 10670

Offset

1,1

Comments

Essentially identical to A022269. - R. J. Mathar, May 28 2008

Links

Table of n, a(n) for n=1..44.

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

Formula

a(n)=(11*n^2+n)/2.

G.f.: x(6+5x)/(1-x)^3. - R. J. Mathar, Oct 23 2008

Example

n=1: 2*n=2, 3*n=3, a(1)=6

Prog

(PARI) a(n)=(11*n^2+n)/2 \\ Charles R Greathouse IV, Jun 17 2017

Crossrefs

Sequence in context: A250647 A304392 A235332 * A022269 A212570 A272840

Adjacent sequences: A026814 A026815 A026816 * A026818 A026819 A026820

Keyword

nonn,easy

Author

Dolmatov S. (aalma(AT)mail.ru), Jun 24 2003

Status

approved