18518

Appears in sequences

• a(n) = floor( (10^n - 1) / (9*n) ).at n=5A089303
• Group the triangular numbers so that the n-th group sum is a multiple of n. 1, (3, 6, 10, 15), (21), (28), (36, 45, 55, 66, 78), (91, 105, 120, 136, 153, 171, 190), ... Sequence contains n-th group sum divided by n.at n=32A114032
• Number of right triangles on an (n+1) X 5 grid.at n=25A189809
• Numbers k such that (28*10^k + 773)/9 is prime.at n=23A275522