# 1000000021

This number is a prime.

The largest prime that can be represented as the sum of two repdigit numbers each consisting of d times each digit d, i.e., 22+999999999. [Loungrides]

A prime that remains prime after inserting the digit X in all internal positions at the same time: 1X0X0X0X0X0X0X0X2X1. This is valid for X=5 and for X=8, producing the following two primes: 1505050505050505251 and 1808080808080808281. [Rivera]

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