A199976 - OEIS

%I #10 Aug 18 2024 16:26:25

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

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

%U 4,8,0,0,4,8,0,0,0,0,0,0,0,1,2,4,5,6

%N Multiplicative digital root of n-th nonprime number.

%F a(n) = A031347(A018252(n)).

%t mdr[n_]:=NestWhile[Times@@IntegerDigits[#]&,n,#>9&]; mdr/@Select[Range[200],!PrimeQ[ #]&] (* _Harvey P. Dale_, Aug 18 2024 *)

%Y Cf.: A199975(n) = multiplicative digital root of n-th prime.

%K nonn,base

%O 1,2

%A _Jaroslav Krizek_, Nov 13 2011