OFFSET
1,3
COMMENTS
First differences of A000050. - Jean-Fran�ois Alcover, Mar 19 2014
REFERENCES
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
Seth A. Troisi, Table of n, a(n) for n = 1..50
Daniel Shanks, The second-order term in the asymptotic expansion of B(x), Math. Comp., 18 (1964), 75-86.
EXAMPLE
a(4)=4 since 2^4=16 and 1=1^2, 5=1^2+2^2, 9=3^2, 13=2^2+3^2.
PROG
(PARI) a(n)=if(n<0, 0, sum(k=1, 2^(n-1), 0<sum(y=0, sqrtint(2*k-1), issquare(2*k-1-y^2))))
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
9 more terms from Sean A. Irvine, Sep 14 2009
STATUS
approved