43920

Appears in sequences

• a(n) = ((p-1)!/(2*p^2)) * Sum_{j=1..p-1} 1/j where p is the n-th prime.at n=2A079303
• Numerators b(n) of Pythagorean approximations b(n)/a(n) to 1/2.at n=12A195548
• Denominators a(n) of Pythagorean approximations b(n)/a(n) to 2.at n=3A195614
• a(n) = Fibonacci(n)*A008653(n) for n>=1, with a(0)=1, where A008653 is the theta series of direct sum of 2 copies of hexagonal lattice.at n=15A205967
• Construct sequences P,Q,R by the rules: Q = first differences of P, R = second differences of P, P starts with 1,3,9, Q starts with 2,6, R starts with 4; at each stage the smallest number not yet present in P,Q,R is appended to R. Sequence gives P.at n=57A225385
• Number of active (ON, black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 801", based on the 5-celled von Neumann neighborhood.at n=7A273574
• T(n,k) is the number of posets of n labeled elements with k covering relations (n>=1, k>=0). Triangle read by rows.at n=24A342589
• a(n) = A000111(n) * A000142(n). Row sums of A373434.at n=6A373433