20221

Appears in sequences

• Numbers k such that 39*2^k + 1 is prime.at n=44A002269
• n written in fractional base 4/2.at n=45A024630
• a(n) = Sum_{i=0..floor(n/2)} T(2i,n-2i), array T as in A049723.at n=33A049726
• Ternary emirpimes.at n=16A119684
• Number of n-node unlabeled rooted trees with thinning limbs and root outdegree (branching factor) 9.at n=13A244710
• Triangle read by rows: T(n,k) is the coefficient A_k in the transformation of 1 + x + x^2 + ... + x^n to the polynomial A_k*(x+3k)^k for 0 <= k <= n.at n=52A248977
• Numbers that require three steps to collapse to a single digit in base 4 (written in base 4).at n=12A253953
• Numbers n with the property that n^2 contains a sequence of four or more consecutive 8's.at n=8A301938
• Expansion of e.g.f. exp(-x * sqrt(1-4*x)).at n=6A362161
• Number of regions in a regular 2n-gon when all vertices are connect by straight lines except for the n lines joining diametrically opposite vertices.at n=14A368813
• Irregular triangle read by rows: T(n,k) is the number of free polyominoes with n cells having k regions between the polyominoes and their bounding boxes, n >= 1, k >= 0.at n=62A380282
• a(n) = (3^(n+2) + 4^(2*n+1))/13.at n=4A386397