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 A386419 #15 Jul 21 2025 13:12:41
%S A386419 1,3,15,45,585,2295,11475,29835,72675,424575,7977165,28851975,
%T A386419 29277885,39317175
%N A386419 Odd numbers k that are closer to being perfect than previous terms, and also satisfy the condition that phi(k) = phi(sigma(k)).
%C A386419 Questions: Is 45 the only term also in A228058? (See also A354362). Are there only multiples of 5 after the two initial terms?
%C A386419 If it exists, a(15) > 2^30 (1073741824).
%H A386419 <a href="/index/O#opnseqs">Index entries for sequences where (the least) odd perfect number must occur</a>
%o A386419 (PARI)
%o A386419 A353680(n) = ((n%2) && (eulerphi(sigma(n))==eulerphi(n)));
%o A386419 isA353679(n) = A353680(n);
%o A386419 m=-1; n=0; k=0; while(m!=0, n++; if(!(n%(2^25)),print1("("n")")); if(isA353679(n), if((m<0) || abs((sigma(n)/n)-2)<m, m=abs((sigma(n)/n)-2); k++; write("b386419.txt", k, " ", n); print1(n, ", "))));
%Y A386419 Subsequence of A353679.
%Y A386419 Cf. A000010, A000203, A000396, A228058, A354362.
%Y A386419 Cf. also A171929, A228059, A386420, A386421, A386422.
%K A386419 nonn,more
%O A386419 1,2
%A A386419 _Antti Karttunen_, Jul 21 2025