19800

Appears in sequences

• Number of walks on square lattice. Column y=3 of A052174.at n=7A005561
• Theta series of A_11 lattice.at n=3A023902
• Theta series of A*_11 lattice.at n=72A023923
• For all n, if d is recursively applied to a(n) exactly 6 times then the fixed point of d-iteration is just reached.at n=31A036458
• Star of David matchstick numbers: a(n) = 6*n*(3*n+1).at n=33A045946
• Composite numbers divisible by the palindromic sum of their prime factors (counted with multiplicity).at n=31A046358
• Composite numbers divisible by the palindromic sum of their palindromic prime factors (counted with multiplicity).at n=18A046366
• a(n) is the cototient of n^3.at n=29A053192
• Totient of 2^n+1.at n=15A053285
• McKay-Thompson series of class 34A for Monster.at n=43A058638
• Numbers k such that sigma (x) = k has exactly 12 solutions.at n=23A060676
• Fourth (unsigned) column of triangle A062138 (generalized a=5 Laguerre).at n=3A062150
• a(n) = A062401(A065391(n)): phi(sigma(m)) peak values for numbers m (listed in A065391) at which those peaks are first reached.at n=22A065392
• Even legs of Pythagorean triangles whose other leg and hypotenuse are both prime.at n=13A067755
• First differences of A069475, successive differences of (n+1)^6-n^6.at n=25A069476
• Numbers k such that 1/(1/phi(k) + 1/phi(k+1) + 1/phi(k+2) + 1/phi(k+3)) is an integer.at n=15A073544
• One half of A075178.at n=19A075179
• Group the natural numbers such that the sum of the terms of every group has a distinct prime signature not occurring earlier: (1), (2), (3, 4, 5), (6), (7, 8, 9), (10, 11, 12, 13, 14), (15, 16, 17), (18, 19, 20, 21)... Sequence contains the sum of the terms of groups.at n=46A086494
• Positive first differences of the rows of triangle A088459, which enumerates symmetric Dyck paths.at n=62A093768
• a(n) = sum along n-th diagonal of A094102 (sloping downward to left).at n=38A094103