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%I #23 Jul 21 2018 17:54:07
%S 1,3,4,7,6,2,8,5,3,8,2,6,4,8,8,3,8,4,0,8,6,8,8,0,3,8,0,0,0,4,6,8,6,0,
%T 6,9,8,0,0,0,8,0,6,6,0,4,6,8,5,4,4,4,0,0,4,0,0,0,0,6,2,0,0,4,6,6,6,2,
%U 0,6,4,0,6,4,8,0,0,6,0,6,2,2,6,6,0,6,0
%N Multiplicative digital root of sigma(n).
%C Multiplicative digital root of A000203(n).
%F a(n) = A031347(A000203(n)).
%e For n = 12: sigma(12) = 28; a(n) = 6 because 2 * 8 = 16; 1 * 6 = 6.
%p m:= n-> `if`(n<10, n, m(mul(d, d=convert(n, base, 10)))):
%p a:= n-> m(numtheory[sigma](n)):
%p seq(a(n), n=1..100); # _Alois P. Heinz_, Jul 21 2018
%o (PARI) a031347(n) = while(n>9, n=prod(i=1, #n=digits(n), n[i])); n;
%o a(n) = a031347(sigma(n)); \\ _Michel Marcus_, Jul 07 2018
%Y Cf. A000203, A031347.
%Y Cf. A190998 (additive digital root of sigma(n)).
%K nonn,base
%O 1,2
%A _Jaroslav Krizek_, Jul 07 2018