a(n) is obtained by starting with 1, sequentially concatenating all decimal numbers up to n, and then, starting from n-1, sequentially concatenating all decimal numbers down to 1.
A173426
a(n) is obtained by starting with 1, sequentially concatenating all decimal numbers up to n, and then, starting from n-1, sequentially concatenating all decimal numbers down to 1.
Terms
- a(0) =1a(1) =121a(2) =12321a(3) =1234321a(4) =123454321a(5) =12345654321
External references
- oeis: A173426