20400

Appears in sequences

• Theta series of 17-dimensional lattice Q_17(6)^{+2}.at n=11A015159
• Theta series of 17-dimensional lattice Q_17(6)^{+6}.at n=33A015161
• Number of reversible strings with n-1 beads of 2 colors. 4 beads are black. String is not palindromic.at n=28A032091
• 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=33A036458
• Number of 2n-bead balanced binary strings of fundamental period 2n, rotationally equivalent to reverse, complement and reversed complement.at n=20A045665
• a(n) is the decimal concatenation of n and n^2.at n=19A053061
• Numbers k such that sigma (x) = k has exactly 11 solutions.at n=25A060678
• Trajectory of 318 under the Reverse and Add! operation carried out in base 4, written in base 10.at n=5A075153
• a(n) = (n-1)(n-4)(n-9)...(n-k^2) where k^2 < n <= (k+1)^2.at n=20A080500
• Numbers n divisible by exactly two nontrivial permutations (rearrangements) of the digits of n.at n=19A090057
• a(n) = sigma_3(n) - sigma_1(n).at n=26A092348
• Number of partitions of n having no doubletons. By a doubleton in a partition we mean an occurrence of a part exactly twice (the partition [4,(3,3),2,2,2,(1,1)] of 18 has two doubletons, shown between parentheses).at n=42A116645
• Numbers n that raised to the powers from 1 to k (with k>=1) are multiple of the sum of their digits (n raised to k+1 must not be a multiple). Case k=8.at n=35A135193
• E.g.f.: A(x) = G(G(x)) where G(x) = x*exp(A(x)) such that G( x*exp(-G(x)) ) = x and G(x) is the e.g.f. of A140054.at n=4A140055
• Terms of A061047 ending in 0.at n=27A146950
• 6 times octagonal numbers: a(n) = 6*n*(3*n-2).at n=34A153796
• Maximum coefficient of the polynomial (-1)^(n+1)*Product_{k=1..n} (1 - x^k)^2.at n=26A156082
• Number of reduced words of length n in Coxeter group on 5 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.at n=7A163878
• Number of reducible Boolean polynomials of degree n.at n=15A169913
• Numbers with prime factorization pqr^2s^4.at n=16A190107