199680

Appears in sequences

• Number of 4-block ordered bicoverings of an unlabeled n-set.at n=27A060091
• a(n) = 2*a(n-1) + 2*a(n-2), a(0)=0, a(1)=4.at n=12A116556
• Triangle read by rows, expansion of exp(x*exp(z)*tan(z)).at n=47A298213
• Denominators of the coefficients in a series for the angles in the Spiral of Theodorus.at n=7A351862
• Index of the closure of a triangle group Delta, associated with billiards in a regular n-gon, in the adelic group Gamma = SL_2(O), where O is the profinite completion of Z[zeta + zeta^{-1}] and zeta is the n-th root of unity.at n=18A374898
• Square array A(n,k) = A388978(A388981(n, k)), read by descending antidiagonals.at n=18A389168