A199975 - OEIS

%I #14 Jul 31 2020 15:13:25

%S 2,3,5,7,1,3,7,9,6,8,3,2,4,2,6,5,0,6,8,7,2,8,8,4,8,0,0,0,0,3,4,3,2,4,

%T 8,5,5,8,8,2,8,8,9,4,8,8,2,2,6,8,8,0,8,0,0,8,0,4,4,6,6,0,0,3,9,2,9,8,

%U 6,0,0,5,2,8,4,4,2,4,0,0,8,8,2,8,0,6

%N Multiplicative digital root of n-th prime.

%H Harvey P. Dale, <a href="/A199975/b199975.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A031347(A000040(n)).

%t Table[s = Prime[n]; While[s >= 10, s = Times @@ IntegerDigits[s]]; s, {n, 100}] (* _T. D. Noe_, Nov 15 2011 *)

%t Table[NestWhile[Times@@IntegerDigits[#]&,p,#>9&],{p,Prime[Range[90]]}] (* _Harvey P. Dale_, Jul 31 2020 *)

%Y Cf. A199976 (multiplicative digital root of n-th nonprime number).

%K nonn,base

%O 1,1

%A _Jaroslav Krizek_, Nov 13 2011