OFFSET
0,1
COMMENTS
a(n)=0 unless n == 0, 1 or 4 (mod 8).
REFERENCES
H. Iwaniec. Spectral methods of automorphic forms, volume 53 of Graduate Studies in Mathematics. American Mathematical Society, Providence, RI, 2002.
LINKS
Robert Israel, Table of n, a(n) for n = 0..10000
Fernando Chamizo, Correlated sums of r(n), J. Math. Soc. Japan, 51(1):237-252, 1999.
Fernando Chamizo, and Roberto J. Miatello, Sums of squares in real quadratic fields and Hilbert modular groups, arXiv preprint arXiv:1812.10725 [math.NT], 2018.
MAPLE
N:= 200: # for a(0)..a(N)
g1:= 1 + 2*add(x^(i^2), i=1..floor(sqrt(N+1))):
g2:= expand(g1^2):
R:= [seq(coeff(g2, x, i), i=0..N+1)]:
seq(R[i]*R[i+1], i=1..N+1); # Robert Israel, Jun 12 2020
MATHEMATICA
a[n_] := SquaresR[2, n] SquaresR[2, n + 1]; a /@ Range[0, 100] (* Giovanni Resta, Jun 12 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 11 2019
STATUS
approved