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 A035527 #16 Jan 05 2025 19:51:35
%S A035527 1,6,28,270,496,672,1638,6200,8128,18620,30240,32760,173600,1089270,
%T A035527 2229500,2457000,4713984,6051500,8506400,17428320,23088800,29410290,
%U A035527 33550336,45532800,52141320,81695250,115048440,142990848,255428096
%N A035527 Harmonic seed numbers.
%C A035527 A harmonic number is a harmonic seed if it does not have a proper unitary divisor (a divisor d such that gcd(d,n/d)=1) which is harmonic.
%H A035527 Donovan Johnson, <a href="/A035527/b035527.txt">Table of n, a(n) for n = 1..138</a> (terms < 10^14)
%H A035527 G. L. Cohen and R. M. Sorli, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Scanned/36-5/cohen.pdf">Harmonic seeds</a>, Fibonacci Quart., 36 No. 5 (1998) 386-390 MR1657575 (99j:11002)
%o A035527 (PARI) harm(n)=if(n<1,0,0==(sigma(n,0)*n)%sigma(n,1))
%o A035527 {a(n)=local(t);if(n<0,0,n=a(n-1); until(if(t=1,if(harm(n), fordiv(n,d, t*=((d==n)||(d==1)||(gcd(d,n/d)!=1)||!harm(d)));t,0)),n++);n)}
%Y A035527 Cf. A001599 for harmonic numbers.
%K A035527 nonn
%O A035527 1,2
%A A035527 _Jeff Burch_
%E A035527 Offset corrected by _Donovan Johnson_, Aug 21 2012