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A321687 a(n) = (2*n+1)-digit palindrome formed by first concatenating A158289(i) for i=1..n+1 and then A158289(n-j) for j=1..n. 0
1, 121, 12321, 1234321, 123454321, 12345654321, 1234567654321, 123456787654321, 12345678987654321, 1234567898987654321, 123456789878987654321, 12345678987678987654321, 1234567898765678987654321, 123456789876545678987654321, 12345678987654345678987654321 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..14.

EXAMPLE

                     1

                    121

                   12321

                  1234321

                 123454321

                12345654321

               1234567654321

              123456787654321

             12345678987654321

            1234567898987654321

           123456789878987654321

          12345678987678987654321

         1234567898765678987654321

        123456789876545678987654321

       12345678987654345678987654321

      1234567898765432345678987654321

     123456789876543212345678987654321

    12345678987654321012345678987654321

   1234567898765432101012345678987654321

  123456789876543210121012345678987654321

PROG

(PARI) a158289(n)=abs(n-round(n/18)*18)

eva(n) = subst(Pol(n), x, 10)

a(n) = if(n==0, return(1)); my(v=vector(2*n+1), x=#v); for(k=1, ceil(#v/2), v[k]=a158289(k)); while(1, v[x]=v[#v-x+1]; x--; if(x==ceil(#v/2), return(eva(v))))

CROSSREFS

Cf. A158289.

Sequence in context: A137466 A062689 A057139 * A002477 A173426 A261570

Adjacent sequences:  A321684 A321685 A321686 * A321688 A321689 A321690

KEYWORD

nonn,base,easy

AUTHOR

Felix Fröhlich, Nov 17 2018

STATUS

approved

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)