28821

Appears in sequences

• Expansion of g.f. 1/(1 - 3*x + 2*x^3).at n=10A077846
• Inverse hyperbinomial transform of A089467.at n=6A089466
• Triangular array read by rows: T(n,k) is the number of functions f:{1,2,...,n} -> {1,2,...,n} that have exactly k 2-cycles for n >= 0 and 0 <= k <= floor(n/2).at n=12A185025
• a(n) = 2*Sum_{k=0..n-1} C(n-1,k)*C(n+k,k) + n.at n=7A236407
• Triangle read by rows: T(n,k) (0 <= k <= n) = Sum_{i=0..[k/2]} (-1)^i*binomial(k,2*i)*(2*i-1)!!*n^(k-2*i).at n=27A244490
• Smallest number k >= A000043(n) such that k*A000668(n)*(k*A000668(n)+1)-1 is prime.at n=25A249509
• Expansion of 1/(1 - Sum_{k>=2} floor(1/omega(k))*x^k), where omega(k) is the number of distinct prime factors (A001221).at n=25A280195
• Number of compositions (ordered partitions) of n into parts with an odd number of distinct prime divisors.at n=25A286224
• Number of compositions (ordered partitions) of n into parts having the same number of distinct prime divisors as n.at n=25A301332
• Array read by antidiagonals: T(n,k) is the number of functions f: X->Y, where X is a subset of Y, |X| = n, |Y| = n+k, such that for every x in X, f(f(x)) != x.at n=34A334014
• a(n) = n * (binomial(n,2) - 2).at n=39A341768