21756

Appears in sequences

• Positive numbers k such that k and 3*k are anagrams in base 8 (written in base 8).at n=13A023074
• Numbers k such that 133*2^k+1 is prime.at n=23A032416
• Numbers k such that k | sigma_7(k) - phi(k)^7.at n=19A055701
• Sum of the elements in the coprime subsets of the integers 1 to n.at n=16A087081
• Volume of the 3-dimensional box of sides of length equal to consecutive Padovan numbers (A000931). These boxes form a spiral in three dimensions similar to the spiral of Fibonacci boxes in two dimensions.at n=12A100538
• a(n) = 4*n*(4*n - 1).at n=37A104188
• a(n) = 25*n^2 + 25*n + 6.at n=29A177059
• v(n+1)/v(n), where v=A203012.at n=2A203158
• Number of partitions of n into distinct parts with boundary size 8.at n=38A227565
• Array read by antidiagonals: T(n,k) = number of lattice paths from (0,0) to (n,k) using steps (1,0), (0,1), (1,1), (-1,1) and whose points lie entirely in the integer rectangle of lattice points {(i, j): 0 <= i <= n, 0 <= j <= k}.at n=50A232968
• Least integer k > 1 such that pi(k)^2 + pi(k*n)^2 is a square, where pi(.) is the prime-counting function given by A000720.at n=32A255677
• Oblong numbers the product of whose digits are positive oblong numbers.at n=13A285079
• Consider Watanabe's 3-shift tag system {00/1011} applied to the word (100)^n; a(n) = position of the longest word in the orbit, or -1 if the orbit is unbounded.at n=36A292094
• Triangle T(m,k) read by rows, where T(m,k) is the number of ways in which 1<=k<=m positions can be picked in an m X m square grid such that the picked positions have a point symmetry or a line symmetry.at n=25A292153
• Total number of divisors d of m (counted with multiplicity), such that the prime signature of d is a partition of four and m runs through the set of least numbers whose prime signature is a partition of n.at n=11A309919
• Sorted areas of primitive Heronian triangles for which a rectangle exists with integer dimensions and with perimeter and area equal respectively to the perimeter and area of the triangle.at n=18A343769
• a(n) is the number of partitions of n in which no part is divisible by 3 minus the number of basis partitions of n.at n=54A350636
• Coefficient of x^n in the expansion of ( 1/(1-x)^2 * (1+x^2) )^n.at n=6A370242