OFFSET
1,1
LINKS
Christopher Heiling, Table of n, a(n) for n = 1..150
FORMULA
a(n) = Sum_{k = 1..n} A000118(k^2).
EXAMPLE
For n = 2 the a(n) = 32 integral solutions of x^2 + y^2 + z^2 + t^2 <= 2^2 are: {x,y,z,t} = {{0,0,0,1}; {0,0,1,0}; {0,1,0,0}; {1,0,0,0}; {0,0,0,-1}; {0,0,-1,0}; {0,-1,0,0}; {-1,0,0,0}; {0,0,0,2}; {0,0,0,-2}; {0,0,2,0}; {0,0,-2,0}; {0,2,0,0}; {0,-2,0,0}; {2,0,0,0}; {-2,0,0,0}; {1,1,1,1}; {1,1,1,-1}; {1,1,-1,1}; {1,-1,1,1}; {-1,1,1,1}; {1,1,-1,-1}; {1,-1,1,-1}; {-1,1,1,-1}; {1,-1,-1,1}; {-1,1,-1,1}; {1,-1,-1,-1}; {-1,1,-1,-1}; {-1,-1,1,-1}; {-1,-1,1,-1}; {-1,-1,-1,1}; {-1,-1,-1,-1}}.
MAPLE
terms := 42:
(add(q^(m^2), m = -terms..terms))^4:
seq(add(coeff(%, q, k^2), k = 1..n), n = 1..terms); # Peter Bala, Jan 15 2016
PROG
(PARI) a000118(k) = if(k<1, k==0, 8 * sumdiv( k, d, if( d%4, d)));
a(n) = sum(k=1, n, a000118(k^2)); \\ Altug Alkan, Jan 19 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Christopher Heiling, Jan 12 2016
STATUS
approved