A086790 a(n) = floor((1+n+2*n^2+4*n^3)/(1+2*n+n^2))

1, 2, 4, 8, 11, 15, 19, 23, 26, 30, 34, 38, 42, 46, 50, 54, 58, 62, 66, 70, 74, 78, 82, 86, 90, 94, 98, 102, 106, 110, 114, 118, 122, 126, 130, 134, 138, 142, 146, 150, 154, 158, 162, 166, 170, 174, 178, 182, 186, 190, 194, 198, 202, 206, 210, 214, 218, 222, 226, 230

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (2,-1).

Formula

a(n) = floor(4*n-6+9/(n+1)-2/(n+1)^2). For n>=8 a(n)=4*n-6 - Benoit Cloitre, Aug 06 2003

Example

a(2)=floor((1+2^1+2*2^2+4*2^3)/(1+2*2^1+2^2))=floor(43/9)=floor(4.77778)=4

Mathematica

LinearRecurrence[{2, -1}, {1, 2, 4, 8, 11, 15, 19, 23, 26, 30}, 60] (* Harvey P. Dale, Jun 20 2020 *)

Prog

(PARI) a(n)=floor(4*n-6+9/(n+1)-2/(n+1)^2) \\ Charles R Greathouse IV, Oct 07 2015

Crossrefs

Sequence in context: A034037 A330331 A033153 * A326299 A320448 A115797

Adjacent sequences: A086787 A086788 A086789 * A086791 A086792 A086793

Keyword

easy,nonn

Author

Wang Dan (wangdan01(AT)lycos.com), Aug 04 2003

Extensions

More terms from Benoit Cloitre, Aug 06 2003

Status

approved