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 A137926 #16 Feb 12 2018 02:50:22
%S A137926 1,1,3,4,5,3,7,1,1,5,11,1,13,7,15,16,17,1,19,5,21,11,23,3,25,13,27,7,
%T A137926 29,15,31,1,33,17,35,4,37,19,39,5,41,21,43,11,5,23,47,3,49,25,51,13,
%U A137926 53,27,55,7,57,29,59,5,61,31,7,64,65,33,67,17,69,35,71,1,73,37,25,19,77,39,79
%N A137926 a(n) = the largest divisor of n that is coprime to A000005(n). (A000005(n) = the number of positive divisors of n.)
%H A137926 Robert Israel, <a href="/A137926/b137926.txt">Table of n, a(n) for n = 1..10000</a>
%e A137926 6 has 4 positive divisors. The divisors of 6 are 1,2,3,6. The divisors of 6 that are coprime to 4 are 1 and 3. 3 is the largest of these; so a(6) = 3.
%p A137926 f := proc (n) local D, t; D := numtheory:-divisors(n); t := nops(D); max(select(proc (d) options operator, arrow; igcd(d, t) = 1 end proc, D)) end proc:
%p A137926 map(f, [$1..100]); # _Robert Israel_, Feb 11 2018
%t A137926 Table[Select[Divisors[n], GCD[ #, Length[Divisors[n]]] == 1 &][[ -1]], {n, 1, 80}] (* _Stefan Steinerberger_, Mar 09 2008 *)
%o A137926 (PARI) a(n) = {my(d = divisors(n)); vecmax(select(x->(gcd(x, #d) == 1), d));} \\ _Michel Marcus_, Feb 12 2018
%Y A137926 Cf. A046642 (a(n)=n), A120737 (a(n)=1), A137927.
%K A137926 nonn
%O A137926 1,3
%A A137926 _Leroy Quet_, Feb 23 2008
%E A137926 More terms from _Stefan Steinerberger_, Mar 09 2008