20559

Appears in sequences

• a(n) = floor(n*(n+2)*(2*n-1)/8).at n=42A007518
• Number of partitions of 1/n into 4 reciprocals of positive integers.at n=24A020327
• Odd 9-gonal (or enneagonal) numbers.at n=38A028991
• a(n) = (2*n+1)*(7*n+1).at n=38A033572
• Numbers k such that 111*2^k-1 is prime.at n=41A050581
• Denominators of convergents to Pi by Farey fractions.at n=49A063673
• Iccanobirt prime indices (1 of 15): Indices of prime numbers in A102111.at n=13A102131
• a(n) = (n+1)*(n+2)*(n+3)*(n+4)*(7*n^2 + 20*n + 15)/360.at n=8A108683
• Enneagonal numbers for which the product of the digits is also an enneagonal number.at n=24A117052
• Triangle read by rows: T(n,k) = p(k)*T(n-1,k) + T(n-1,k-1) (1 <= k <= n), where p(k) denotes the k-th prime.at n=41A124960
• a(1)=1. Thereafter, a(n) = n*a(n-1) if the number of divisors of n*a(n-1) is <= the number of divisors of n+a(n-1) or a(n) = n+a(n-1) if n*a(n-1) has more divisors than n+a(n-1).at n=19A134189
• a(n) = Sum_{k=0..floor(n/2)} binomial(n-k,k)^(k+1) * n/(n-k).at n=7A181071
• Principal diagonal of the convolution array A213564.at n=8A213565
• a(0)=a(1)=1, a(n) = least k > a(n-1) such that k*a(n-2) is a triangular number.at n=34A214961
• Number of ways of writing n as the sum of 7 triangular numbers.at n=44A226252
• Arises from color-symmetrized counting of tensor invariants.at n=6A232220
• Sum of the smallest parts of the partitions of 4n into 4 parts.at n=19A238702
• Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 563", based on the 5-celled von Neumann neighborhood.at n=26A272941
• Squarefree terms of A276655.at n=25A276756
• a(n) = n*(n + 1)*(4*n + 5)/2.at n=21A281381