20553

Appears in sequences

• a(n) = floor( n*(n-1)*(n-2)*(n-3)/32 ).at n=30A011942
• Nonsquares with A072594(n) = 0.at n=36A072596
• Non-palindromic numbers n such that phi(n) = phi(reversal(n)).at n=19A097647
• Numbers k such that sigma(k) - phi(k) is a 4th power.at n=24A115918
• Numbers k such that k + sigma(k) + sigma(sigma(k)) is a square.at n=39A116014
• Number of ways to place zero or more nonadjacent 0,0 1,0 2,0 2,1 2,2 3,1 4,2 polyhexes in any orientation on a planar nXnXn triangular grid.at n=7A155323
• Number of 6-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero and first differences in -n..n.at n=7A208997
• Number of (w,x,y,z) with all terms in {1,...,n} and w+x=|x-y|+|y-z|.at n=34A212676
• Squarefree numbers which yield zero when their prime factors are xored together.at n=11A235488
• 27-gonal pyramidal numbers: a(n) = n*(n+1)*(25*n-22)/6.at n=17A256647
• Where the first 3n primes are partitioned into 3 sets of cardinality n, the minimum of the largest product.at n=3A260075
• Number of compositions of n with strictly increasing differences.at n=46A325547