A108336 Unique sequence of 1's and 0's such that (Sum_{n >= 0} a(n)*x^n)^2 mod 4 has coefficients which are all 1's and 2's (A083952).

1, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0

Offset

0,1

Comments

Equals A084202 read mod 2.

Links

Robert Israel, Table of n, a(n) for n = 0..10000

N. Heninger, E. M. Rains and N. J. A. Sloane, On the Integrality of n-th Roots of Generating Functions, arXiv:math/0509316 [math.NT], 2005-2006.

N. Heninger, E. M. Rains and N. J. A. Sloane, On the Integrality of n-th Roots of Generating Functions, J. Combinatorial Theory, Series A, 113 (2006), 1732-1745.

Maple

S:= 0: SS:= 0:
for i from 0 to 100 do
  s:= coeff(SS, x, i);
  if s = 0 or s = 3 then
     SS:= SS + 2*expand(S*x^i)+x^(2*i) mod 4; S:= S + x^i;
  fi
od:
seq(coeff(S, x, i), i=0..100); # Robert Israel, May 14 2019

Mathematica

max = 98; (* a = A084202 *) a[n_] := a[n] = Block[{s = Sum[a[i]*x^i, {i, 0, n-1}]}, If[IntegerQ @ Last @ CoefficientList[Series[Sqrt[s + x^n], {x, 0, n}], x], 1, 2]]; Table[a[n], {n, 0, max}]; A108336 = CoefficientList[ Series[Sqrt[Sum[a[i]*x^i, {i, 0, max}]], {x, 0, max}], x] // Mod[#, 2]& (* Jean-François Alcover, Apr 01 2016, after Robert G. Wilson v *)

Crossrefs

Cf. A083952, A084202, A108335, A108337, A108340.

Sequence in context: A093075 A104120 A254634 * A279733 A176723 A189126

Adjacent sequences: A108333 A108334 A108335 * A108337 A108338 A108339

Keyword

nonn,easy,nice

Author

N. J. A. Sloane and Nadia Heninger, Jul 02 2005

Status

approved