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!)
 A211415 Number of ordered triples (w,x,y) with all terms in  {-n,...,0,...,n} and w^2 + x*y = 1. 3
 0, 12, 20, 36, 52, 68, 84, 100, 132, 148, 164, 180, 212, 228, 244, 276, 308, 324, 340, 356, 388, 420, 436, 452, 516, 532, 548, 564, 596, 612, 644, 660, 692, 724, 740, 772, 804, 820, 836, 868, 932, 948, 980, 996, 1028, 1060, 1076, 1092, 1156, 1172 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS For n>0, a(n)+2 is the number of self-inverse 2 X 2 matrices with all terms in {-n,...,0,...,n} (see A211416). For a guide to related sequences, see A211422. LINKS Chai Wah Wu, Table of n, a(n) for n = 0..10000 FORMULA For n>0, a(n+1) - a(n) = 8*A060594(n+1). - Pontus von BrÃ¶mssen, Jan 22 2020 MATHEMATICA t[n_] := t[n] = Flatten[Table[w^2 + x*y - 1, {w, -n, n}, {x, -n, n}, {y, -n, n}]] c[n_] := Count[t[n], 0] t = Table[c[n], {n, 0, 20}]  (* A211415 *) t + 2                        (* A211416 *) (t + 2)/2    (* integers *) t/4          (* integers *) (t/4 - 1)/4  (* integers for n>1 *) PROG (MAGMA) a:=[]; for n in [0..50] do Append(~a, #[:w, x, y in [-n..n]|w^2 + x*y eq 1]); end for; a; // Marius A. Burtea, Jan 22 2020 CROSSREFS Cf. A060594, A211416, A211422. Sequence in context: A082296 A187766 A260905 * A209973 A282754 A063690 Adjacent sequences:  A211412 A211413 A211414 * A211416 A211417 A211418 KEYWORD nonn AUTHOR Clark Kimberling, Apr 09 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 August 2 14:18 EDT 2021. Contains 346428 sequences. (Running on oeis4.)