A111355 Consider the sequence defined in A083952 as a binary string of the digits 1 and 2. Then a(n) is the beginning position of the first occurrence of exactly 2n-1 consecutive 2's.

2, 4, 222, 154, 754, 204, 14, 246, 1300, 3642

Offset

1,1

Comments

Strings of ones are always isolated and at an odd position.

Links

Table of n, a(n) for n=1..10.

Mathematica

a[0] = 1; a[l_] := a[l] = Block[{k = 1, s = Sum[ a[i]*x^i, {i, 0, l - 1}]}, While[ IntegerQ[ Last[ CoefficientList[ Series[(s + k*x^l)^(1/2), {x, 0, l}], x]]] != True, k++ ]; k]; p = Flatten[ Position[ Table[ a[n], {n, 0, 4150}], 1]]; f[n_] := Block[{k = n, m = 1}, While[m < Length[p] && p[[m + 1]] - p[[m]] != n, m++ ]; If[m < Length[p] - k, p[[m]] + 1, 0]]; Table[ f[2n], {n, 10}]

Crossrefs

Cf. A083952.

Sequence in context: A116010 A018677 A173637 * A018706 A111162 A018715

Adjacent sequences: A111352 A111353 A111354 * A111356 A111357 A111358

Keyword

nonn

Author

Paul D. Hanna and Robert G. Wilson v, Nov 08 2005

Status

approved