31320

Appears in sequences

• a(n) = floor(n*(n-1)*(n-2)*(n-3)/21).at n=30A011931
• Nonunitary doubly perfect numbers: the sum of the nonunitary divisors of n is 2n; i.e., sigma(n) - usigma(n) = 2n.at n=1A064592
• Nontrivial nonunitary multiply perfect numbers: the sum of the nonunitary divisors of n is a positive multiple of n; i.e., (sigma(n) - usigma(n))/n is a positive integer.at n=4A064595
• 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=33A066460
• Numbers k not in A065036 but such that tau(k) = omega(k)^3.at n=31A074853
• (prime(n-1) + 1)*(prime(n+1) - 1).at n=39A087105
• Numbers k such that k^2 is a palindrome when written in base 17.at n=42A118651
• Coordination sequence for 8-dimensional cyclotomic lattice Z[zeta_15].at n=6A126898
• a(n) is the smallest number m such that sigma(m)=n*pi(m), or 0 if no such m exists.at n=30A137602
• Number of ways to place 4 nonattacking wazirs on an n X n board.at n=5A172227
• The number of permutations p of {1,...,n} satisfying |p(i)-p(i+1)| is in {4,5} for i from 1 to n-1.at n=41A174708
• Triangle T(n, m) = ( |-A008292(n+1,m+1)^2 + 2*binomial(n, m)^2| + A008292(n+1,m+1)*binomial(n, m) )/2 read by rows.at n=29A178048
• Triangle T(n, m) = ( |-A008292(n+1,m+1)^2 + 2*binomial(n, m)^2| + A008292(n+1,m+1)*binomial(n, m) )/2 read by rows.at n=34A178048
• Sum of divisors of the product of two consecutive primes.at n=39A180617
• Numbers with prime factorization p*q*r^3*s^3 (where p, q, r, s are distinct primes).at n=12A190108
• Number of n X 4 0..1 arrays avoiding 0 0 1 and 1 0 0 horizontally and 0 0 1 and 1 0 1 vertically.at n=14A209646
• Triangle read by rows: T(n,k) = number of n X n binary matrices with k pairwise nonadjacent 1's, n >= 0, k = 0..n^2.at n=65A232833
• a(n) = n!*(e*Gamma(n,1)*(n-1)+1).at n=4A262601
• The least positive integer that has exactly n different representations as Brazilian number.at n=32A284758
• Numbers k for which A306927(k) [= A001615(k)-k] is a multiple of A344705(k) [= A001615(k)-A001065(k)], and their quotient is nonnegative.at n=39A344700