140450

Appears in sequences

• a(n) = -(u^n-1)*(v^n-1) with u = 2+sqrt(3), v = 2-sqrt(3).at n=8A129743
• Continued fraction expansion for exp( Sum_{n>=1} 1/(n*A003500(n)) ), where A003500(n) = (2+sqrt(3))^n + (2-sqrt(3))^n.at n=17A174500
• Numbers n (other than powers of 2) such that abs(abundance(n)) is an odd square.at n=5A188484
• Number of perfect matchings in the graph C_4 X C_n.at n=6A220864
• Numbers k such that sigma(k) + tau(k) + phi(k) is a prime, where sigma(k) = A000203(k), tau(k) = A000005(k) and phi(k) = A000010(k).at n=21A229265
• Number of perfect matchings in the graph C_9 X C_{2n}.at n=0A281583
• Expansion of Product_{k>=1} 1/(1 - x^k)^tau_k(k), where tau_k(k) = number of ordered k-factorizations of k (A163767).at n=16A304965