23486

Appears in sequences

• a(n) = (n+1)*a(n-1) + (2-n)*a(n-2).at n=7A006183
• Triangular array generated by its row sums: T(n,0) = 1 for n >= 0, T(n,1) = r(n-1), T(n,k) = T(n,k-1) - (-1)^k * r(n-k) for k = 2, 3, ..., n, n >= 2, r(h) = sum of the numbers in row h of T.at n=47A054090
• T(n,2), array T as in A054090.at n=7A054096
• Semiprimes in A054552.at n=25A113690
• a(0)=2, a(1)=3, a(n) = 3 + a(n-1) + a(n-2) for n >= 2.at n=18A171237
• Number of length n+5+2 0..5 arrays with every value 0..5 appearing at least once in every consecutive 5+3 elements, and new values 0..5 introduced in order.at n=4A242320
• T(n,k)=Number of length n+k+2 0..k arrays with every value 0..k appearing at least once in every consecutive k+3 elements, and new values 0..k introduced in order.at n=40A242322
• Number of (n+2) X (2+2) 0..4 arrays with every consecutive three elements in every row and column not having exactly two distinct values, and in every diagonal and antidiagonal having exactly two distinct values, and new values 0 upwards introduced in row major order.at n=10A252805
• a(1) = 1; a(n) = Sum_{k=1..n} a(ceiling((n-1)/k)).at n=42A290845
• Expansion of 1/(1 + x*Product_{k>=1} (1 - x^k)).at n=33A331484
• a(n) = Sum_{j=1..n} Sum_{k=1..n} tau(j*k).at n=43A372674