|
| |
|
|
A000076
|
|
Number of integers <= 2^n of form 4 x^2 + 4 x y + 5 y^2.
(Formerly M1079 N0409)
|
|
1
|
|
|
|
0, 0, 1, 2, 4, 7, 14, 24, 43, 82, 149, 284, 534, 1015, 1937, 3713, 7136, 13759, 26597, 51537, 100045, 194586, 378987, 739161, 1443465, 2821923, 5522689
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
0,4
|
|
|
REFERENCES
|
D. Shanks and L. P. Schmid, Variations on a theorem of Landau. Part I, Math. Comp., 20 (1966), 551-569.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
|
|
|
LINKS
|
Table of n, a(n) for n=0..26.
Index entries for sequences related to populations of quadratic forms
|
|
|
EXAMPLE
|
a(4)=4 since 2^4=16 and 4=4*1^2, 5=5*1^2, 13=4*1^2+4*1*1+5*1^2, 16=4*2^2.
|
|
|
PROG
|
(PARI) a(n)=if(n<0, 0, sum(k=1, 2^n, 0<sum(j=0, sqrtint(k)\2, issquare(k-4*j^2)&(k-j)%2==0)))
|
|
|
CROSSREFS
|
Sequence in context: A000075 A048248 A056180 * A217730 A218576 A054169
Adjacent sequences: A000073 A000074 A000075 * A000077 A000078 A000079
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
N. J. A. Sloane.
|
|
|
STATUS
|
approved
|
| |
|
|
