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 A366991 #10 Apr 22 2025 05:21:32
%S A366991 1,2,2,3,2,4,2,4,3,4,2,6,2,4,4,4,2,6,2,6,4,4,2,8,3,4,4,6,2,8,2,5,4,4,
%T A366991 4,9,2,4,4,8,2,8,2,6,6,4,2,8,3,6,4,6,2,8,4,8,4,4,2,12,2,4,6,5,4,8,2,6,
%U A366991 4,8,2,12,2,4,6,6,4,8,2,8,4,4,2,12,4,4
%N A366991 The number of divisors of n that are not terms of A322448.
%C A366991 First differs from A365680 at n = 64.
%C A366991 The number of divisors of n whose prime factorization has exponents that are all either 1 or primes.
%C A366991 The sum of these divisors is A366992(n) and the largest of them is A366994(n).
%H A366991 Amiram Eldar, <a href="/A366991/b366991.txt">Table of n, a(n) for n = 1..10000</a>
%F A366991 Multiplicative with a(p^e) = A000720(e) + 2.
%F A366991 a(n) <= A000005(n), with equality if and only if n is a biquadratefree number (A046100).
%t A366991 f[p_, e_] := PrimePi[e] + 2; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100]
%o A366991 (PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, primepi(f[i, 2]) + 2);}
%Y A366991 Cf. A000005, A000720, A046100, A365680, A366989, A366992, A366994.
%K A366991 nonn,easy,mult
%O A366991 1,2
%A A366991 _Amiram Eldar_, Oct 31 2023