18688

Appears in sequences

• tanh(arctan(x)*tan(x))=2/2!*x^2-80/6!*x^6-2688/8!*x^8+18688/10!*x^10...at n=4A012451
• a(n) = Sum_{k >= 1} floor(2*tau^(n-k)).at n=17A020957
• Triangle read by rows: T(n,k) (n >= 2, 0 <= k <= n) = number of over-all crude totals of unbranched k-5-catapolyheptagons.at n=38A038195
• Primitive numbers k that divide sigma(k)*phi(k).at n=13A055196
• From expansion of Belyi function for octahedron.at n=4A066405
• Numbers k such that h(k) = h(k-1) + h(k-2), where h(k) = A006577(k) + 1 is the length of the sequence {k, f(k), f(f(k)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=33A078418
• Numbers n such that h(n) = 2 h(n-1) where h(n) is the length of the sequence {n, f(n), f(f(n)), ...., 1} in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)at n=37A078419
• a(1) = 1, a(2) = 2; for n >= 2, a(n+1) = a(n) + sum of the unique prime factors of a(n).at n=24A096460
• G.f.: (1+14*x+x^2)^3/((1-x))^4.at n=4A113922
• Smallest number m such that prime(n) is a factor of both m and sigma(m).at n=20A156099
• a(n) = 73*n^2.at n=16A174334
• Products of the 8th power of a prime and a distinct prime (p^8*q).at n=20A179668
• Number of ways to place n nonattacking composite pieces rook + rider[3,6] on an n X n chessboard.at n=7A189860
• a(n) = Product_{k>=1} floor(n^(1/k)).at n=72A190668
• Monotonic ordering of set S generated by these rules: if x and y are in S then x^2+y^2-xy is in S, and 2 is in S.at n=22A192533
• Number of (n+1)X8 0..1 arrays with the number of rightwards and downwards edge increases in each 2X2 subblock differing from the number in all its horizontal and vertical neighbors.at n=10A205071
• Number of nX6 0..1 arrays avoiding 0 0 1 and 1 0 1 horizontally and 0 1 0 and 1 0 1 vertically.at n=4A207252
• T(n,k)=Number of nXk 0..1 arrays avoiding 0 0 1 and 1 0 1 horizontally and 0 1 0 and 1 0 1 vertically.at n=49A207254
• Number of 5 X n 0..1 arrays avoiding 0 0 1 and 1 0 1 horizontally and 0 1 0 and 1 0 1 vertically.at n=5A207256
• Records in A114183.at n=16A222193