21294

Appears in sequences

• Write 1, 2, 3, 4, ... counterclockwise in a hexagonal spiral around 0 starting left down, then a(n) is the sequence found by reading from 0 in the vertical upward direction.at n=42A063436
• a(n) = n^2*(n+1)*(2*n+1)/3.at n=12A098077
• a(n) = 14*n^2.at n=39A144555
• E.g.f.: A(x) = 1 + Sum_{n>=1} (1/n!)*Product_{k=1..n} -log(1 - k(k+1)x/2).at n=5A171779
• Successive integers produced by Conway's PRIMEGAME using Kilminster's Fractran program with only nine fractions.at n=39A183132
• Molecular topological indices of the sunlet graphs.at n=20A192846
• Number of (w,x,y,z) with all terms in {1,...,n} and w>2x and y>3z.at n=28A212518
• Triangle read by rows: T(n,k) is the number of ascent sequences of length n with last zero at position k-1.at n=51A218579
• Number of nX1 0..3 arrays with exactly floor(nX1/2) elements equal to at least one king-move neighbor, with new values introduced in row major 0..3 order.at n=10A222604
• Smallest area A of Heron triangles with sides (a, b, c) in arithmetic progression of the form b - d(n), b, b + d(n), where d(n) = A091998(n) = 12*n +- 1.at n=28A229098
• Triangle read by rows: T(n,k) is the number of k-element equivalence classes of closed meanders with 2n points.at n=15A339460
• Number T(n,k) of endofunctions on [n] with exactly k isolated fixed points; triangle T(n,k), n >= 0, 0 <= k <= n, read by rows.at n=50A350212
• a(n) = A003961(n) * sigma(A003961(n)), where A003961 is fully multiplicative with a(p) = nextprime(p), and sigma is the sum of divisors function.at n=43A361467
• Number of partitions of n with at least three parts larger than 1.at n=37A362548