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 A225648 #17 Mar 03 2016 02:25:12
%S A225648 0,1,5,7,8,9,11,13,17,19,23,27,29,31,37,41,43,47,53,59,61,67,71,73,79,
%T A225648 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
%U A225648 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313
%N A225648 Positions of ones in A225650, numbers n such that n and A000793(n) are coprime.
%C A225648 Contains all primes from 5 onward. Are 8, 9 and 27 only composite numbers present?
%H A225648 Alois P. Heinz, <a href="/A225648/b225648.txt">Table of n, a(n) for n = 1..5000</a>
%t A225648 b[n_, i_] := b[n, i] = Module[{p}, p = If[i < 1, 1, Prime[i]]; If[n == 0 || i < 1, 1, Max[b[n, i - 1], Table[p^j*b[n - p^j, i - 1], {j, 1, Log[p, n] // Floor}]]]]; g[n_] := b[n, If[n < 8, 3, PrimePi[Ceiling[1.328*Sqrt[n* Log[n] // Floor]]]]]; Join[{0}, Position[Table[GCD[n, g[n]], {n, 1, 500} ], 1] // Flatten] (* _Jean-François Alcover_, Mar 03 2016, after _Alois P. Heinz_ *)
%o A225648 (Scheme with _Antti Karttunen_'s IntSeq-library):
%o A225648 (define A225648 (MATCHING-POS 1 1 (lambda (i) (= 1 (gcd (A000793 i) i)))))
%Y A225648 Complement: A225649. Cf. also A225650.
%K A225648 nonn
%O A225648 1,3
%A A225648 _Antti Karttunen_, May 12 2013