A057139 Odd number of digits palindrome based on sequential digits.

1, 121, 12321, 1234321, 123454321, 12345654321, 1234567654321, 123456787654321, 12345678987654321, 1234567890987654321, 123456789010987654321, 12345678901210987654321, 1234567890123210987654321, 123456789012343210987654321, 12345678901234543210987654321

Offset: 1

Author

Henry Bottomley, Aug 12 2000

Keywords

• base
• easy
• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..100

Crossrefs

Alternative progression for n >= 10 compared with A002477.

Cf. A057137, A057138.

Programs

Mathematica

Array[FromDigits@ Join[#, Reverse@ Most@ #] &@ Mod[Range[#], 10] &, 15] (* Michael De Vlieger, Jan 28 2020 *)

PARI

a(n)={fromdigits(vector(2*n-1, i, if(i<=n, i, 2*n-i)%10))} \\ Andrew Howroyd, Jan 27 2020

Formula

a(n) = 10^n*A057137(n-1) + A057138(n) = 10^(n-1)*A057137(n) + A057138(n-1).

Extensions

Terms a(13) and beyond from Andrew Howroyd, Jan 27 2020