A224336 Number of idempotent 5 X 5 0..n matrices of rank 4.

155, 805, 2555, 6245, 12955, 24005, 40955, 65605, 99995, 146405, 207355, 285605, 384155, 506245, 655355, 835205, 1049755, 1303205, 1599995, 1944805, 2342555, 2798405, 3317755, 3906245, 4569755, 5314405, 6146555, 7072805, 8099995, 9235205, 10485755, 11859205, 13363355

Offset: 1

Author

R. H. Hardin, formula via M. F. Hasler _William J. Keith_ and Rob Pratt in the Sequence Fans Mailing List, Apr 03 2013

Keywords

• nonn
• easy
• changed

Examples

			Some solutions for n=3:
..1..0..0..1..0....0..0..0..0..0....0..2..3..2..2....1..0..0..1..0
..0..1..0..1..0....1..1..0..0..0....0..1..0..0..0....0..1..0..2..0
..0..0..1..2..0....3..0..1..0..0....0..0..1..0..0....0..0..1..2..0
..0..0..0..0..0....2..0..0..1..0....0..0..0..1..0....0..0..0..0..0
..0..0..0..2..1....3..0..0..0..1....0..0..0..0..1....0..0..0..1..1
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210
• Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

Crossrefs

Row 5 of A224333.

Programs

PARI

Vec(-5*x*(x^4-6*x^3+16*x^2+6*x+31)/(x-1)^5 + O(x^100)) \\ Colin Barker, Sep 20 2014

Formula

a(n) = 10*n^4 + 40*n^3 + 60*n^2 + 40*n + 5.

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5). - Colin Barker, Sep 20 2014

G.f.: -5*x*(x^4-6*x^3+16*x^2+6*x+31) / (x-1)^5. - Colin Barker, Sep 20 2014

E.g.f.: 5*(exp(x)*(1 + 30*x + 50*x^2 + 20*x^3 + 2*x^4) - 1). - Stefano Spezia, Aug 25 2025