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A259937 Concatenation of the numbers from 1 to n with numbers from n down to 1. 4
11, 1221, 123321, 12344321, 1234554321, 123456654321, 12345677654321, 1234567887654321, 123456789987654321, 1234567891010987654321, 12345678910111110987654321, 123456789101112121110987654321 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n < 700, only a(1) and a(10) are primes.

LINKS

Table of n, a(n) for n=1..12.

FORMULA

a(n) = A007908(n) concatenated with A000422(n).

EXAMPLE

a(1)=11;

a(5)=1234554321.

MATHEMATICA

FromDigits /@ Flatten /@ IntegerDigits /@ (#~Join~Reverse@ # & /@ Table[Range@ n, {n, 12}]) (* Michael De Vlieger, Jul 10 2015 *)

PROG

(PARI)  a(n)=r=""; for(i=0, n-1, r=concat(n-i, concat(r, n-i))); r; \\ Anders Hellström, Aug 16 2015

CROSSREFS

Cf. A000422, A007908, A244861.

Sequence in context: A019524 A274766 A261138 * A078269 A015009 A068326

Adjacent sequences:  A259934 A259935 A259936 * A259938 A259939 A259940

KEYWORD

nonn,base

AUTHOR

José de Jesús Camacho Medina, Jul 09 2015

STATUS

approved

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Last modified October 18 11:56 EDT 2018. Contains 316321 sequences. (Running on oeis4.)