10000...00303 (100-digits)

This number is a prime.

                                            1000000000 0000000000 0000000000
0000000000 0000000000 0000000000 0000000000 0000000000 0000000000 0000000303

10^99+303 is the smallest 100-digit prime whose sum of digits equals the prime 7. [Bajpai]