A214506 Last digit of the smallest prime number in base 10 with n digits.

2, 1, 1, 9, 7, 3, 3, 9, 7, 7, 9, 3, 9, 7, 1, 7, 1, 3, 3, 1, 9, 7, 9, 7, 7, 3, 7, 3, 1, 9, 7, 3, 9, 1, 3, 9, 7, 3, 3, 3, 1, 9, 3, 7, 1, 9, 1, 3, 3, 9, 1, 1, 7, 1, 1, 1, 3, 9, 9, 9, 7, 3, 7, 1, 7, 9, 9, 9, 9, 9, 3, 3, 9, 9, 7, 9, 3, 1, 3, 9, 9, 3, 1, 7, 1, 3

Offset: 1

Author

Tjandra Satria Gunawan, Jul 19 2012

Keywords

• nonn
• base

Comments

The last digit of the first prime number in base 10 with n digits for n = 1, 2, 3 is 211, because 2 is the least with 1 digit, 11 the least with 2 digits, 101 the least with 3 digits. The concatenation, 211, is prime. This does not happen again through 24 digits. - Jonathan Vos Post, Jul 04 2012

Programs

Mathematica

Table[Mod[NextPrime[10^n],10],{n,0,30}] (* Harvey P. Dale, Jan 25 2013 *)

Formula

a(1) = 2, and a(n) = A033873(n) mod 10 for n>1.

a(n) = A003617(n) mod 10. - Michel Marcus, Aug 06 2013

Extensions

More terms from Harvey P. Dale, Jan 25 2013