18810

Appears in sequences

• a(n) = n*(n + 1)*(3*n + 1).at n=18A027903
• Numbers k whose decimal representation, read as a base-19 value and divided by k, yields an integer.at n=13A032569
• Number of nonempty subsets of {1,2,...,n} in which exactly 5/6 of the elements are <= (n-2)/2.at n=26A047192
• Numbers k such that k | sigma_7(k) - phi(k)^7.at n=18A055701
• Composite numbers k such that the difference between the odd and even aliquot parts of k divides k.at n=22A066193
• Numbers n such that sigma(n)/phi(n) is prime.at n=32A067780
• Numbers k such that phi(k) = sigma(core(k)) where phi(k) is the Euler totient function, sigma(k) the sum of divisors of k and core(k) the squarefree part of k (the smallest integer such that k*core(k) is a square).at n=9A069552
• 2*Jacobsthal(n-1)*Fibonacci(n).at n=10A093045
• Smallest n-digit triangular number - smallest n-digit number.at n=17A095865
• Determinant of the 2 X 2 matrices where the first column is consecutive triangular numbers and the second column is the corresponding consecutive Fibonacci numbers.at n=13A113772
• a(n) = (n+1)(n+2)^2*(n+3)^2*(n+4)(2n+5)/720.at n=7A114242
• Triangle read by rows: T(n,k) = binomial(n-1,k-1)*binomial(n,k-1)/k + binomial(n-1,k)*binomial(n,k)/(k+1) (1 <= k <= n). In other words, to each entry of the Narayana triangle (A001263) add the entry on its right.at n=58A118976
• Triangle read by rows: T(n,k) = binomial(n-1,k-1)*binomial(n,k-1)/k + binomial(n-1,k)*binomial(n,k)/(k+1) (1 <= k <= n). In other words, to each entry of the Narayana triangle (A001263) add the entry on its right.at n=61A118976
• Array of T(n,m)=1*5*...*(4n-3)*3*7*...*(4m-1)*2^(n+m)/(n+m)! by antidiagonals.at n=41A122882
• Composite numbers such that the square root of the sum of squares of their prime factors is a prime.at n=12A134607
• Riordan array (1, x(1 - 4x)/(1 - 7x + 3x^2)).at n=30A147723
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 0), (-1, 0, 0), (0, 1, -1), (0, 1, 1), (1, -1, 0)}.at n=9A148868
• Numbers n such that n^2 can be represented as sum of (at least two) consecutive cubes and n is not a triangular number.at n=26A163393
• Number of nX2 1..3 arrays containing at least one of each value, all equal values connected, rows considered as a single number in nondecreasing order, and columns considered as a single number in increasing order.at n=19A166814
• Numbers n such that sigma(n) = 13*phi(n) (where sigma=A000203, phi=A000010).at n=3A171258