A138793 a(n) = concatenation of reversed digits of natural numbers from n down to 1.

1, 21, 321, 4321, 54321, 654321, 7654321, 87654321, 987654321, 1987654321, 1101987654321, 211101987654321, 31211101987654321, 4131211101987654321, 514131211101987654321, 61514131211101987654321, 7161514131211101987654321

Offset: 1

Author

Artur Jasinski, Mar 30 2008, Apr 04 2008

Keywords

• nonn
• easy
• base

Comments

Note that leading zeros are not omitted when writing down digits in reversed order. So 10 reversed becomes 01. - N. J. A. Sloane, Jan 23 2017

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A104759, A000422, A116504, A007908, A116505, A104759, A138789, A138790.

Programs

Magma

[Seqint(&cat[Reverse(Intseq(k)): k in [1..n]]): n in [1..16]]; // Bruno Berselli, May 27 2011

Maple

read(transforms): A138793 := proc(n) return digrev(parse(cat($(1..n)))): end: seq(A138793(n),n=1..17); # Nathaniel Johnston, Jun 26 2011

Mathematica

b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[AppendTo[a, w[[k]]], {k, 1, Length[w]}]; p = FromDigits[Reverse[a]]; AppendTo[b, p], {n, 1, 61}]; b (* Artur Jasinski, Mar 30 2008 *)
lst = {}; Table[FromDigits[Reverse[lst = Join[lst, IntegerDigits[n]]]], {n, 1, 15}] (* Robert Price, Mar 22 2015 *)

PARI

a(n) = my(s = ""); forstep (k=n,1,-1, sk = digits(k); forstep (j=#sk, 1, -1, s = concat(s, sk[j]))); eval(s); \\ Michel Marcus, Jan 28 2017