20124

Appears in sequences

• Number of permutations of [n] with four inversions.at n=22A005287
• Number of lines through exactly 4 points of an n X n grid of points.at n=40A018811
• Numbers k such that sigma(phi(k)) = phi(sigma(k)).at n=11A033632
• Decimal part of cube root of a(n) starts with 2: first term of runs.at n=26A034128
• Numbers k such that phi(2*sigma(k)) = 2*sigma(phi(k)).at n=13A067709
• Numbers k such that sigma(phi(k)) divides phi(sigma(k)).at n=21A073858
• Sum of numbers that can be written as t*n + u*(n+1) for nonnegative integers t,u in exactly four ways.at n=7A076457
• Trajectory of n under the Reverse and Add! operation carried out in base 3 (presumably) does not reach a palindrome and (presumably) does not join the trajectory of any term m < n.at n=45A077405
• Numbers k such that sigma(phi(k)) == phi(sigma(k)) (mod k), that is, A033632(k)/k is an integer.at n=13A092584
• Number of Abelian cubefree words over a 3-letter alphabet.at n=10A096168
• Triangle read by rows: T(n,k) is the number of Schroeder paths of length 2n and having k valleys.at n=40A101282
• Number of reduced words of length n in the Weyl group A_25.at n=4A161525
• Number of nX3 binary arrays without the pattern 0 1 0 diagonally, vertically or horizontally.at n=5A188502
• Number of nX6 binary arrays without the pattern 0 1 0 diagonally, vertically or horizontally.at n=2A188505
• T(n,k)=Number of nXk binary arrays without the pattern 0 1 0 diagonally, vertically or horizontally.at n=30A188508
• T(n,k)=Number of nXk binary arrays without the pattern 0 1 0 diagonally, vertically or horizontally.at n=33A188508
• Number of 2n-bead necklaces labeled with numbers 1..6 allowing reversal, with neighbors differing by exactly 1.at n=10A208669
• Number of partitions of n into distinct parts with boundary size 10.at n=33A227567
• n^2 * a(n) = 6*(66*n^2 - 94*n + 41) * a(n-1) - 36*(2016*n^2 - 5712*n + 4387) * a(n-2) + 50544*(132*n^2 - 560*n + 609) * a(n-3) - 7884864*(6*n-17)^2*a(n-4), with a(0)=1, a(1)=78, a(2)=4446, a(3)=20124.at n=3A276177
• Smallest k for which a chain of linked rods of length 1, ..., k can be folded in half in exactly n dictinct ways.at n=33A390056