A166923 Digital root of prime(n)^2.

4, 9, 7, 4, 4, 7, 1, 1, 7, 4, 7, 1, 7, 4, 4, 1, 7, 4, 7, 1, 1, 4, 4, 1, 4, 4, 7, 1, 1, 7, 1, 7, 4, 7, 7, 4, 7, 1, 7, 4, 1, 1, 4, 7, 1, 1, 7, 4, 4, 7, 1, 7, 4, 1, 7, 4, 1, 1, 4, 4, 7, 7, 1, 7, 4, 4, 4, 7, 7, 4, 4, 1, 4, 7, 1, 7, 4, 1, 7, 7, 7, 4, 1, 1, 4, 4, 1, 4, 4, 7, 1, 4, 1, 7, 7, 1, 7, 1, 1, 1, 4, 1, 7, 4, 7

Offset: 1

Author

Zak Seidov, Oct 23 2009

Keywords

• base
• nonn

Crossrefs

Cf. A010888, A038194.

Programs

Mathematica

Table[If[(m9=Mod[Prime[n]^2,9])==0,9,m9],{n,200}]

Python

from sympy import prime
def A166923(n):
    return 1 + (prime(n)**2-1) % 9 # Chai Wah Wu, Sep 03 2014

Extensions

Definition corrected by Chai Wah Wu, Sep 03 2014