21420

Appears in sequences

• a(n) = n*(n+1)*(n+2)/2.at n=34A027480
• a(n) = lcm(n,n+1,n+2).at n=33A033931
• Triangle of coefficients arising in calculation of A002872 and A002874 (sorting numbers).at n=40A036073
• Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= (n-1)/3.at n=23A048012
• Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= (n-2)/3.at n=23A048023
• Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= (n-3)/3.at n=23A048034
• a(n) in base 13 is a repdigit.at n=45A048337
• Golden rectangular box numbers: a(n) = n*A007067(n)*A007067(A007067(n)).at n=17A050510
• Number of 4-element ordered antichains on an unlabeled n-element set; T_1-hypergraphs with 4 labeled nodes and n hyperedges.at n=3A056069
• a(n) = 9*binomial(n,4) = 3*n*(n-1)*(n-2)*(n-3)/8.at n=17A060008
• a(n) = lcm(3n+1, 3n+2, 3n+3).at n=11A061495
• a(n) is the least positive integer k such that k is a repdigit number in exactly n different bases B, where 1<B<k.at n=37A066460
• Numbers k such that k^2 + 1 is composite and phi(k^2 + 1) == 0 (mod k).at n=33A067519
• Numbers occurring twice in A068627.at n=21A068628
• One half of A075178.at n=33A075179
• Numbers k such that the total number of 1's in the binary expansion of all the divisors of k sets a new record.at n=31A093687
• Number of edges in LCM of graphs K_n and C_4.at n=34A098585
• Integers that can be expressed as a product of triangular numbers in 3 different ways.at n=4A110904
• Triangle read by rows: T(n,k) is the number of Motzkin paths of length n having k UDH's starting at level 0 (U=(1,1),H=(1,0),D=(1,-1)).at n=53A114581
• Triangle read by rows: T(i,j) = F(i)*F(j)*C(i,j) for 1 <= j <= i, where F(n) is the n-th Fibonacci number and C(n,m) is a binomial coefficient.at n=40A117965