21480

Appears in sequences

• Number of oriented graphs (i.e., digraphs with no bidirected edges) on n unlabeled nodes. Also number of complete digraphs on n unlabeled nodes. Number of antisymmetric relations (i.e., oriented graphs with loops) on n unlabeled nodes is A083670.at n=5A001174
• Numbers k such that k! - 1 is prime.at n=21A002982
• Number of regions in regular n-gon with all diagonals drawn.at n=29A007678
• Number of ordered 5-tuples of integers from [ 1,n ] with no common factors among triples.at n=21A015656
• dot_product(n,n-1,...2,1)*(7,8,...,n,1,2,3,4,5,6).at n=38A026066
• Number of partitions satisfying cn(0,5) <= cn(1,5) + cn(4,5) + cn(2,5) + cn(3,5).at n=36A039849
• A088258 indexed by A000142.at n=38A088412
• Triangle of T(n,k)=number of peakless Motzkin paths of length n containing k valleys (can be easily expressed using RNA secondary structure terminology).at n=45A089738
• Array read by antidiagonals: T(n,k) = number of n-step knight's tours on a (k+2)X(k+2) board summed over all starting positions.at n=40A186851
• Number of 5-step knight's tours on an (n+2) X (n+2) board summed over all starting positions.at n=4A186854
• Total number of parts in all partitions of n with at least one distinct part.at n=25A220477
• Number of ways to write highly composite numbers (A002182(n)) as the difference of two primes, both <= 2*A002182(n).at n=37A228945
• Smallest number k such that R(n) is the n-th divisor of k, where R(n) is the n-th Ramanujan prime (A104272).at n=15A233933
• Number T(n,k) of sets of nonempty words with a total of n letters over k-ary alphabet such that for k>0 the k-th letter occurs at least once and within each word every letter of the alphabet is at least as frequent as the subsequent alphabet letter; triangle T(n,k), n>=0, 0<=k<=n, read by rows.at n=42A319498
• Numbers that are not Keith numbers in any base.at n=29A320122
• Expansion of Product_{k>=1} 1/((1 - x^k) * (1 - x^(2*k)) * (1 - x^(3*k)) * (1 - x^(4*k)) * (1 - x^(5*k))).at n=22A327044
• Indices of unique values in A329152.at n=24A333268
• Place two n-gons with radii 1 and 2 concentrically, forming an annular area between them. Connect all the vertices with line segments that lie entirely within that area. Then a(n) is the number of regions in that figure.at n=27A337700
• Numbers k such that A348215(k) = k.at n=34A348216
• Indices where prime(n) first appears in A373902.at n=35A371618