18777

Appears in sequences

• a(n) = Sum_{i=1..n-1} a(i)*a(n-1-i), with a(0) = 1, a(1) = 3.at n=9A014432
• Duplicate of A014432.at n=9A025236
• Number of permutations of length n which avoid the patterns 1234, 3421, 4312.at n=30A116756
• Odd integers that do not generate monotonically decreasing infinitary aliquot sequences.at n=38A127667
• a(n)=sum{k=0..n, C(n,floor(k/2))*(-1)^k*4^(n-k)}.at n=7A133444
• The number of binary pattern classes in the (2,n)-rectangular grid with 6 '1's and (2n-6) '0's: two patterns are in same class if one of them can be obtained by a reflection or 180-degree rotation of the other.at n=11A228581
• Number of n X 6 0..2 arrays with no element equal to one plus the sum of elements to its left or one plus the sum of elements above it or one plus the sum of the elements diagonally to its northwest, modulo 3.at n=21A239359
• Numbers k such that 7*10^k + 13 is prime.at n=16A274676
• Number of set partitions of [n] such that the difference between each element and its block index is a multiple of four.at n=18A274837
• The sum a(n) + a(n+1) is visible around the comma that follows a(n+1). See the Comments and Example sections for details.at n=9A334829
• a(n) = Sum_{k=3..n} binomial(k-1,2) * floor(n/k).at n=46A366970