This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
G.f. = -1 + x + x^3 + x^4 + x^6 + x^7 + 2*x^8 + x^9 + x^10 + x^12 + x^13 + 2*x^14 + ...
a020944 n = a020944_list !! n a020944_list = -1 : f [1,0] where f (x:y:xs) = x : f (y:xs ++ [x,x+y]) -- Same list generator function as for a020951_list, cf. A020951. -- Reinhard Zumkeller, Mar 13 2013
a[ n_] := Which[ n < 2, Boole[n == 1] - Boole[n == 0], OddQ[n], Abs[a[n - 1] - a[n - 2]], True, a[n/2] + a[n/2 - 1]]; (* Michael Somos, Jul 25 2018 *)
{a(n) = if( n<2,(n==1) - (n==0), n%2, abs( a(n-1) - a(n-2) ), a(n/2) + a(n/2 - 1) )}; /* Michael Somos, Jan 08 2011 */
{a(n) = my(A, m); if( n<0, 0, m = 1; A = -1 + O(x); while( m <= n, m*=2; A = 2*x + (1 + x + x^2) * subst( A, x, x^2 ) ); polcoeff( A, n ) )}; /* Michael Somos, Jan 08 2011 */
a082498 n = a082498_list !! n a082498_list = 0 : 1 : concat (zipWith (\u v -> [u, u + v]) (tail a082498_list) a082498_list) -- Reinhard Zumkeller, Jul 19 2013
a(n) = if(n<2,n,if(n%2==0,a(n/2),a((n-1)/2)+a((n-3)/2)))
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