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 A369427 #7 Jan 24 2024 12:18:52
%S A369427 0,0,0,1,0,0,0,0,1,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,1,0,0,1,0,0,0,0,0,0,
%T A369427 0,2,0,0,0,0,0,0,0,1,1,0,0,0,1,1,0,1,0,0,0,0,0,0,0,1,0,0,1,0,0,0,0,1,
%U A369427 0,0,0,1,0,0,1,1,0,0,0,0,0,0,0,1,0,0,0
%N A369427 The number of unitary divisors of n that are squares of primes.
%C A369427 The number of exponents in the prime factorization of n that are equal to 2.
%H A369427 Amiram Eldar, <a href="/A369427/b369427.txt">Table of n, a(n) for n = 1..10000</a>
%F A369427 Additive with a(p^e) = 1 if e = 2, and 0 otherwise.
%F A369427 a(n) > 0 if and only if n is in A038109.
%F A369427 a(A061742(n)) = n, and a(k) < n for all k < A061742(n).
%F A369427 Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{p prime} (1/p^2 - 1/p^3) = A085548 - A085541 = 0.27748478074162196208... .
%t A369427 f[p_, e_] := If[e == 2, 1, 0]; a[1] = 0; a[n_] := Plus @@ f @@@ FactorInteger[n]; Array[a, 100]
%o A369427 (PARI) a(n) = vecsum(apply(x -> if(x == 2, 1, 0), factor(n)[, 2]));
%Y A369427 Cf. A001248, A038109, A056169, A056170, A061742, A085541, A085548.
%Y A369427 Similar sequences: A125070, A293439, A366074, A367512, A369426, A369428.
%K A369427 nonn,easy
%O A369427 1,36
%A A369427 _Amiram Eldar_, Jan 23 2024