2,3

Odd Catalan number is A038003[n] = A000108[2^n-1] = binomial(2^(n+1)-2, 2^n-1)/(2^n).

There is no a(1) because A038003[1] = 1.

a(2) = 1 because A038003[2] = 5 square-free.

a(3) = 1 because A038003[3] = 429 = 3*11*13 square-free.

a(4) = 3 because A038003[4] = 9694845 = 3^2*5*17*19*23*29.

Cf. A038003, A000108.

Sequence in context: A110440 A135574 A008969 this_sequence A153257 A002185 A002589

Adjacent sequences: A119905 A119906 A119907 this_sequence A119909 A119910 A119911

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Aug 02 2006