18136

Appears in sequences

• If p(k) is the k-th prime, then the n-th set of 3 consecutive cousin prime pairs starts at p(a(n)).at n=23A095970
• Numbers n such that (n + prime(n)), (n+1 + prime(n+1)), (n+2 + prime(n+2)) and (n+3 + prime(n+3)) are divisible by 5.at n=10A107582
• Number of connected (3,n)-hypergraphs (without empty edges).at n=6A114935
• Constant term of the reduction by x^2 -> x+1 of the polynomial p(n,x) defined below in Comments.at n=15A192421
• Number of rooted trees with n nodes such that no more than two subtrees corresponding to children of any node have the same number of nodes.at n=14A213920
• Fundamental discriminants of real quadratic number fields with class number 9.at n=19A218159
• Number of nX2 0..3 arrays with exactly floor(nX2/2) elements unequal to at least one horizontal or vertical neighbor, with new values introduced in row major 0..3 order.at n=8A222270
• T(n,k) = Number of n X k 0..3 arrays with exactly floor(n X k/2) elements unequal to at least one horizontal or vertical neighbor, with new values introduced in row major 0..3 order.at n=46A222275
• T(n,k)=Number of nXk 0..3 arrays with exactly floor(nXk/2) elements unequal to at least one horizontal, diagonal or antidiagonal neighbor, with new values introduced in row major 0..3 order.at n=53A222500
• Numbers n such that the sum of first n nontrivial prime powers (A025475 excluding 1) is divisible by n.at n=9A225792
• The 60-degree spoke (or ray) of a hexagonal spiral of Ulam.at n=39A244802
• Expansion of Product_{k>0} ((1-x^{5k-2}) * (1-x^{5k-3})/((1-x^{5k-1}) * (1-x^{5k-4})))^4 in powers of x.at n=36A285444
• a(n) is the number of vertices formed by n-secting the angles of a nonagon (enneagon).at n=33A335782
• Square array T(n,k), n >= 0, k >= 0, read by antidiagonals downwards, where T(n,k) = n! * Sum_{j=0..floor(n/2)} (k/2)^j * (j+1)^(n-j-1) / (j! * (n-2*j)!).at n=51A362377
• E.g.f. satisfies A(x) = exp(x + 3*x^2/2 * A(x)).at n=6A362380
• Triangular array read by rows. T(n,k) is the number of binary relations R on [n] such that the unique idempotent in {R^i:i>=1} contains exactly k non-arcless strongly connected components, n>=0, 0<=k<=n.at n=12A370464