This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A316570 #23 Jul 21 2018 17:54:07 %S A316570 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 A316570 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 A316570 0,6,4,0,6,4,8,0,0,6,0,6,2,2,6,6,0,6,0 %N A316570 Multiplicative digital root of sigma(n). %C A316570 Multiplicative digital root of A000203(n). %F A316570 a(n) = A031347(A000203(n)). %e A316570 For n = 12: sigma(12) = 28; a(n) = 6 because 2 * 8 = 16; 1 * 6 = 6. %p A316570 m:= n-> `if`(n<10, n, m(mul(d, d=convert(n, base, 10)))): %p A316570 a:= n-> m(numtheory[sigma](n)): %p A316570 seq(a(n), n=1..100); # _Alois P. Heinz_, Jul 21 2018 %o A316570 (PARI) a031347(n) = while(n>9, n=prod(i=1, #n=digits(n), n[i])); n; %o A316570 a(n) = a031347(sigma(n)); \\ _Michel Marcus_, Jul 07 2018 %Y A316570 Cf. A000203, A031347. %Y A316570 Cf. A190998 (additive digital root of sigma(n)). %K A316570 nonn,base %O A316570 1,2 %A A316570 _Jaroslav Krizek_, Jul 07 2018