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 A370858 #4 Mar 04 2024 08:47:44
%S A370858 1,2,3,4,7,8,15,24,43,56,111,132,263,420,723,1040,2079,2472,4943,7448,
%T A370858 13091,19236,38471,45884,86119,138024,248459,359142,718283,764160,
%U A370858 1528319,2605756,4858899,7109964,13809075,16009784,32019567,52524888,95697787,125396930
%N A370858 Let L_1 = (1) and L_2 = (1, 2); for any n > 2, L_n is obtained by inserting one n between each pair of consecutive terms of L_{n-1} coprime to n; a(n) gives the number of terms in L_n.
%H A370858 Rémy Sigrist, <a href="/A370858/a370858.gp.txt">PARI program</a>
%F A370858 a(p) = 2*a(p-1) - 1 for any odd prime number p.
%e A370858 The first terms, alongside the corresponding lists, are:
%e A370858 n a(n) L n
%e A370858 - ---- ---------------------------------------------
%e A370858 1 1 (1 )
%e A370858 2 2 (1, 2)
%e A370858 3 3 (1, 3, 2)
%e A370858 4 4 (1, 4, 3, 2)
%e A370858 5 7 (1, 5, 4, 5, 3, 5, 2)
%e A370858 6 8 (1, 6, 5, 4, 5, 3, 5, 2)
%e A370858 7 15 (1, 7, 6, 7, 5, 7, 4, 7, 5, 7, 3, 7, 5, 7, 2)
%o A370858 (PARI) See Links section.
%Y A370858 Cf. A370857 (first differences).
%K A370858 nonn
%O A370858 1,2
%A A370858 _Rémy Sigrist_, Mar 03 2024