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 A227270 #11 Jul 28 2025 17:12:24
%S A227270 1,2,4,6,8,12,16,18,24,32,36,42,48,54,64,72,84,96,108,126,128,144,162,
%T A227270 168,192,216,252,256,288,294,324,336,378,384,432,486,504,512,576,588,
%U A227270 648,672,756,768,864,882,972,1008,1024,1134,1152,1176,1296,1344,1458
%N A227270 Numbers m such that Sum_{i= 1..k} 1/d(i) + Product_{i= 1..k} 1/d(i) = 1, where d(i) are the k prime distinct divisors of m.
%H A227270 Harvey P. Dale, <a href="/A227270/b227270.txt">Table of n, a(n) for n = 1..500</a>
%e A227270 42 is in the sequence because the prime divisors of 42 are 2, 3, 7 and 1/2 + 1/3 + 1/7 + 1/(2*3*7) = 1.
%p A227270 with(numtheory):for n from 1 to 5000 do: x:=factorset(n):n1:=nops(x): d:= sum('1/x[i] ', 'i'=1..n1) + product('1/x[j] ', 'j'=1..n1):if d=1 then printf(`%d, `,n):else fi:od:
%t A227270 pdd1Q[n_]:=Module[{c=FactorInteger[n][[All,1]]},Total[1/c]+ 1/Times@@c ==1]; Join[{1},Select[Range[1500],pdd1Q]] (* _Harvey P. Dale_, Aug 22 2016 *)
%Y A227270 Cf A069819.
%K A227270 nonn,easy
%O A227270 1,2
%A A227270 _Michel Lagneau_, Jul 04 2013