login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A219744 The number of 2 X 2 symmetric positive definite matrices whose entries are integers x,y,z satisfying x^2 + y^2 + z^2 <= n^2. 1
0, 1, 10, 22, 49, 92, 150, 227, 328, 449, 609, 792, 1017, 1281, 1582, 1911, 2308, 2750, 3241, 3778, 4420, 5049, 5776, 6572, 7429, 8378, 9413, 10505, 11646, 12935, 14251, 15690, 17235, 18854, 20580, 22391, 24330, 26352, 28541, 30750 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
MAPLE
a:=proc(n)
local x, y, z, count, num;
count:=0;
for x from 0 to n do
for y from 0 to n do
for z from -n to n do
if x^2+y^2+z^2 > n^2 then next; fi;
if x>0 and x*y > z^2 then count:=count+1; fi;
od:
od:
od:
count;
end:
CROSSREFS
Cf. A219693.
Sequence in context: A216048 A079861 A014008 * A246419 A039315 A225708
KEYWORD
nonn
AUTHOR
W. Edwin Clark, Nov 26 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 16 18:51 EDT 2024. Contains 371750 sequences. (Running on oeis4.)