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

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A209993 Number of 2 X 2 matrices with all elements in {0,1,...,n} and determinant in {-1,0,1}. 0
 1, 16, 45, 94, 159, 248, 349, 478, 623, 792, 973, 1182, 1423, 1672, 1933, 2238, 2559, 2888, 3261, 3630, 4063, 4504, 4925, 5374, 5935, 6456, 6957, 7534, 8159, 8728, 9453, 10062, 10767, 11480, 12141, 12942, 13855, 14584, 15325, 16174, 17183 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS See A210000 for a guide to related sequences. LINKS MATHEMATICA a = 1; b = n; z1 = 40; t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]] c[n_, k_] := c[n, k] = Count[t[n], k] c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, 1}] Table[c1[n, 1], {n, 0, z1}]   (* A209992 *) CROSSREFS Cf. A210000. Sequence in context: A221593 A300962 A051868 * A322343 A345754 A318093 Adjacent sequences:  A209990 A209991 A209992 * A209994 A209995 A209996 KEYWORD nonn AUTHOR Clark Kimberling, Mar 18 2012 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 December 5 10:11 EST 2021. Contains 349543 sequences. (Running on oeis4.)