login
This site is supported by donations to The OEIS Foundation.

 

Logo

The submissions stack has been unacceptably high for several months now. Please voluntarily restrict your submissions and please help with the editing. (We don't want to have to impose further limits.)

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A197168 Number of 2 X 2 integer matrices with elements from {1,...,n} whose determinant is 2. 4
0, 2, 6, 18, 30, 50, 70, 98, 118, 162, 198, 226, 270, 338, 366, 426, 486, 554, 622, 682, 726, 842, 926, 986, 1062, 1202, 1270, 1362, 1470, 1562, 1678, 1802, 1878, 2066, 2158, 2250, 2390, 2602, 2694, 2818, 2974, 3114, 3278, 3434, 3526, 3786, 3966, 4090, 4254, 4490 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

It is also the number of 2 X 2 integer matrices with elements from {1,...,n} whose determinant is -2.

LINKS

Table of n, a(n) for n=1..50.

MATHEMATICA

Table[cnt = 0; Do[If[a*d-b*c == 2, cnt++], {a, n}, {b, n}, {c, n}, {d, n}]; cnt, {n, 50}] (* T. D. Noe, Oct 11 2011 *)

CROSSREFS

Sequence in context: A185382 A257065 A066286 * A034881 A146345 A064842

Adjacent sequences:  A197165 A197166 A197167 * A197169 A197170 A197171

KEYWORD

nonn

AUTHOR

Aldo González Lorenzo, Oct 10 2011

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified August 28 03:16 EDT 2015. Contains 261112 sequences.