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

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

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. 6
0, 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

0,3

COMMENTS

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

LINKS

Chai Wah Wu, Table of n, a(n) for n = 0..10000

FORMULA

a(n) = A209973(n) - 4*n - 2 for n >= 2. - Chai Wah Wu, Nov 28 2016

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 * A277200 A277324 A034881

Adjacent sequences:  A197165 A197166 A197167 * A197169 A197170 A197171

KEYWORD

nonn,changed

AUTHOR

Aldo González Lorenzo, Oct 10 2011

EXTENSIONS

a(0) added by Chai Wah Wu, Nov 27 2016

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 11 06:55 EST 2016. Contains 279043 sequences.