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A138793 a(n) = concatenation of reversed digits of natural numbers from n down to 1. 17
1, 21, 321, 4321, 54321, 654321, 7654321, 87654321, 987654321, 1987654321, 1101987654321, 211101987654321, 31211101987654321, 4131211101987654321, 514131211101987654321, 61514131211101987654321, 7161514131211101987654321 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

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 *)

PROG

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

(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

CROSSREFS

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

Sequence in context: A260487 A057138 A104759 * A014925 A000422 A060554

Adjacent sequences:  A138790 A138791 A138792 * A138794 A138795 A138796

KEYWORD

nonn,easy,base

AUTHOR

Artur Jasinski, Mar 30 2008, Apr 04 2008

STATUS

approved

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Last modified May 26 09:12 EDT 2017. Contains 287093 sequences.