1391720

Appears in sequences

• a(1) = 1; for n>1, sum of binomial(n,k) as k runs over RRS(n), the reduced residue system of n.at n=21A056188
• Number of invertible circulant (0,1) matrices over the reals that have even determinant.at n=21A086479
• Number of polynomials of the form x^n +- x^(n-1) +- x^(n-2) +- ... +- 1 irreducible over the integers.at n=20A087481
• a(n) = 2^(n-1) - binomial(n, floor(n/2)).at n=21A093387