OFFSET
0,2
COMMENTS
a(n) = A323689(n^2) for n >= 0.
LINKS
Paul D. Hanna, Table of n, a(n) for n = 0..100
FORMULA
a(n) = [x^(n^2)] Sum_{k>=0} (x^k + i)^k / (1 + i*x^k)^(k+1) for n > 0.
a(n) = [x^(n^2)] Sum_{k>=0} (x^k - i)^k / (1 - i*x^k)^(k+1) for n > 0.
a(n) = [x^(n^2)] Sum_{n>=0} (-i)^n * (1 + i*x^n)^(2*n+1) / (1 + x^(2*n))^(n+1) for n > 0.
a(n) = [x^(n^2)] Sum_{n>=0} i^n * (1 - i*x^n)^(2*n+1) / (1 + x^(2*n))^(n+1) for n > 0.
EXAMPLE
The generating function of A323689 is
G(x) = Sum_{n>=0} (x^n + i)^n / (1 + i*x^n)^(n+1),
in which the constant term is taken to be 1, so that
G(x) = 1 + 3*x - 14*x^3 + 13*x^4 + 22*x^5 - 30*x^7 - 82*x^8 + 101*x^9 - 46*x^11 + 170*x^12 + 54*x^13 - 524*x^15 + 31*x^16 + 70*x^17 - 78*x^19 + 442*x^20 + 1236*x^21 - 94*x^23 - 3204*x^24 + 1785*x^25 - 2428*x^27 + 842*x^28 + 118*x^29 - 126*x^31 + 6208*x^32 + 4228*x^33 - 14508*x^35 + 10359*x^36 + ...
This sequence gives the odd coefficients of x^n, which occur at n = k^2 for k >= 0.
PROG
(PARI) {A323689(n) = my(SUM = sum(m=0, n, (x^m + I +x*O(x^n))^m / (1 + I*x^m +x*O(x^n))^(m+1) ) ); polcoeff(1 + SUM - I^n/(1+I), n)}
{a(n) = A323689(n^2)}
for(n=0, 30, print1(a(n), ", "))
(PARI) {A323689(n) = my(SUM = sum(m=0, n, (-I)^m*(1 + I*x^m +x*O(x^n))^(2*m+1) / (1 + x^(2*m) +x*O(x^n))^(m+1) ) ); polcoeff(1 + SUM - I^n/(1-I), n)}
{a(n) = A323689(n^2)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Feb 14 2019
STATUS
approved