A137287 - OEIS

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A137287

a(n) is the number 2 written (prime(n)-1)/2 times followed by the digit 1; a(1)=2.

2, 21, 221, 2221, 222221, 2222221, 222222221, 2222222221, 222222222221, 222222222222221, 2222222222222221, 2222222222222222221, 222222222222222222221, 2222222222222222222221, 222222222222222222222221, 222222222222222222222222221, 222222222222222222222222222221

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OFFSET

1,1

COMMENTS

Sum of digits of a(n) = prime(n).

LINKS

Table of n, a(n) for n=1..17.

FORMULA

A007953(a(n)) = A000040(n). - Michel Marcus, Mar 15 2022

EXAMPLE

prime(7)=17; (17-1)/2=8; a(7) = 222222221, 8*"2" concatenated with "1".

PROG