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 A332268 #26 Jul 30 2022 12:45:10 %S A332268 1,2,2,3,2,4,2,4,3,4,1,6,1,3,3,4,1,6,1,6,4,2,1,8,2,2,4,4,1,7,1,4,2,2, %T A332268 3,9,1,2,2,8,1,7,1,3,5,2,1,9,2,5,2,3,1,8,2,5,2,2,1,11,1,2,6,4,2,4,1,3, %U A332268 2,6,1,12,1,2,3,3,2,4,1,9,5,2,1,10,2,2 %N A332268 a(n) is the number of divisors of n that are Niven numbers. %C A332268 If p is a prime number, p >= 11, then a(p) = 1. %C A332268 Numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20, 21, 24, 27, 36, 40, 54, 63, 72, 81, 108, 162, 216, 243, 324, 486, 648, 972, 1944, have all divisors Niven numbers. There are only finitely many numbers all of whose divisors are Niven numbers. (A337741). %C A332268 A333456(n) is the least number k such that a(k) = n. - _Bernard Schott_, Jul 30 2022 %H A332268 Giovanni Resta, <a href="/A332268/b332268.txt">Table of n, a(n) for n = 1..10000</a> %F A332268 a(A333456(n)) = n. - _Bernard Schott_, Jul 30 2022 %e A332268 For n = 4 the divisors are 1, 2, 4 and they are all Niven numbers, so a(4) = 3. %e A332268 For n = 14 the divisors are 1, 2, 7 and 14. Only 1, 2 and 7 are Niven numbers, so a(14) = 3. %t A332268 a[n_] := DivisorSum[n, 1 &, Divisible[#, Plus @@ IntegerDigits[#]] &]; Array[a, 100] (* _Amiram Eldar_, May 04 2020 *) %o A332268 (Magma) [#[d:d in Divisors(k)|d mod &+Intseq(d) eq 0]:k in [1..100]]; %o A332268 (PARI) a(n) = sumdiv(n, d, !(d % sumdigits(d))); \\ _Michel Marcus_, May 04 2020 %Y A332268 Cf. A000005, A005349, A333456, A337741, A340637. %K A332268 nonn,base %O A332268 1,2 %A A332268 _Marius A. Burtea_, May 04 2020