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 A180252 #22 Sep 28 2020 01:04:24
%S A180252 1,2,4,5,8,10,16,17,20,25,32,34,37,40,50,64,68,74,80,85,100,101,125,
%T A180252 128,136,148,160,170,185,197,200,202,250,256,257,272,289,296,320,340,
%U A180252 370,394,400,401,404,425,500,505,512,514
%N A180252 Numbers where all prime divisors are of the form k^2+1.
%H A180252 Ivan Neretin, <a href="/A180252/b180252.txt">Table of n, a(n) for n = 1..10000</a>
%F A180252 Sum_{n>=1} 1/a(n) = Product_{p in A002496} p/(p-1) = Product_{k in A005574} (1 + 1/k^2) = 2.809865... - _Amiram Eldar_, Sep 27 2020
%e A180252 a(17) = 74 because 74 = 2*37 = (1^2+1)*(6^2+1).
%p A180252 with(numtheory):T:=array(1..50):U:=array(1..1000):k:=1:for m from 1 to 300
%p A180252 do:x:=m^2+1:if type(x,prime)=true then T[k]:=x:k:=k+1:else fi:od:for x from
%p A180252 2 to 2000 do: B:=factorset(x):yy:=nops(B):A:=convert(T, set):if A intersect
%p A180252 B = B then printf(`%d, `, x):else fi:od:
%t A180252 Select[Range@520, And @@ IntegerQ /@ Sqrt[FactorInteger[#][[All, 1]] - 1] &] (* _Ivan Neretin_, Aug 31 2016 *)
%Y A180252 Cf. A002496, A002522, A005574.
%K A180252 nonn
%O A180252 1,2
%A A180252 _Michel Lagneau_, Jan 20 2011