21340

Appears in sequences

• Positive numbers k such that k and 2*k are anagrams in base 6 (written in base 6).at n=24A023064
• a(n) = s(1)*s(n) + s(2)*s(n-1) + ... + s(k)*s(n+1-k), where k = floor((n+1)/2), s = (odd natural numbers).at n=39A024598
• a(n) = s(1)s(n) + s(2)s(n-1) + ... + s(k)s(n-k+1), where k = floor(n/2), s = (odd natural numbers).at n=38A025112
• Denominators of continued fraction convergents to sqrt(486).at n=3A041927
• Positive integers n such that the difference between the n-th prime and the sum of the divisors of n is congruent to 1 (mod n).at n=13A111359
• a(n) = n*(8*n^2 + 1)/3.at n=20A143166
• a(n) = 4*n*(4*n^2 + 1).at n=11A144965
• Nonnegative integers m such that m^2 = (a^2-1)*(b^2+1) for some integers a,b.at n=43A174134
• a(n) = n*(n+1)*(2*n+1)/6 - n*floor(n/2).at n=39A178946
• Number of (w,x,y,z) with all terms in {1,...,n} and 2|w-x|>=n+|y-z|.at n=20A212688
• Triangle where the g.f. of row n is: Sum_{k=0..n^2-n+1} T(n,k)*y^k = (2*(1+y)^n - 1) * ((1+y)^n - 1)^(n-1) / y^(n-1), as read by rows.at n=20A220265
• Number of n X 2 0..3 arrays with no element equal to zero plus the sum of elements to its left or one plus the sum of elements above it or one plus the sum of the elements diagonally to its northwest or one plus the sum of the elements antidiagonally to its northeast, modulo 4.at n=43A239594
• Number of partitions p = [x(1), ..., x(k)], where x(1) >= x(2) >= ... >= x(k), of n such that min(x(i) - x(i-1)) is not a part of p.at n=37A241761
• Number of unlabeled rooted trees with n nodes such that the minimal outdegree of inner nodes equals 8.at n=46A244462
• Row sums of the triangular array at A249057.at n=8A249059
• Number of n X 4 binary arrays with rows and columns lexicographically nondecreasing and row and column sums nonincreasing.at n=34A266543
• Total number of sequences with p_j copies of j and longest increasing subsequence of length k summed over all partitions [p_1, p_2, ..., p_k] of n into distinct parts.at n=11A268700
• Number of inequivalent (modulo C_4 rotations) square n X n grids with squares coming in two colors and three squares have one of the colors.at n=7A275799
• Number of compositions (ordered partitions) of n into distinct parts such that number of parts is even.at n=30A332305
• a(n) = Sum_{k=1..n} phi(gcd(k, n))^3.at n=45A342535