A135020 Each natural number is followed by its reversal.

1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 1, 11, 11, 12, 21, 13, 31, 14, 41, 15, 51, 16, 61, 17, 71, 18, 81, 19, 91, 20, 2, 21, 12, 22, 22, 23, 32, 24, 42, 25, 52, 26, 62, 27, 72, 28, 82, 29, 92, 30, 3, 31, 13, 32, 23, 33, 33, 34, 43, 35, 53, 36, 63, 37, 73, 38, 83, 39, 93

Offset: 1

Author

Rolf Pleisch, Feb 10 2008

Keywords

• easy
• nonn
• base
• look

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A004086.

Programs

Mathematica

{#,IntegerReverse[#]}&/@Range[40]//Flatten (* Harvey P. Dale, Aug 17 2025 *)

Formula

a(n) = (n+1)/2 for n = odd, a(n) = A004086(n/2) for n = even.