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 A102642 #12 Nov 27 2021 11:06:31
%S A102642 2,3,5,5,4,5,3,4,4,5,3,7,3,6,3,3,4,6,3,6,4,7,3,6,3,5,3,5,4,7,3,5,4,5,
%T A102642 5,7,3,6,5,5,3,6,3,6,5,5,3,7,3,5,4,5,3,6,7,3,6,3,3,4,3,5,4,3,4,6,3,5,
%U A102642 5,6,3,7,3,5,7,5,5,6,3,5,6,5,3,4,3,5,3,6,3,5,3,5,4,5,5,5,4,6,4,7,3,6,3,4,7
%N A102642 a(n) = A102640(n) + A102641(n) - 1.
%C A102642 A006530(2^n)=2 is a local minimum. Actual sequence displays the "width of valley" between the two nearest peaks of largest prime divisors. At the bottom of valley lies the number 2, the minimum.
%e A102642 n=12: 2^10=4096. The greatest prime divisors of numbers around 4096 [both downward and upward] are as follows: {31, 4093, 89, 13, 2, 241, 683, 4099, 41}. The length of relevant sequence, i.e., between peaks 4093 and 4099 is 7, thus a(12)=7.
%t A102642 With[{nn = 12, lim = 105}, Map[Total@ # - 1 &, Transpose@ {Table[Function[k, 1 + LengthWhile[#, # > 0 &] &@ Differences@ Array[FactorInteger[#][[-1, 1]] &, nn, k]][2^n], {n, lim}], Table[Function[k, 1 + LengthWhile[#, # > 0 &] &@ Differences@ Table[FactorInteger[m][[-1, 1]], {m, k, k - nn, -1}]][2^n], {n, lim}]}]] (* _Michael De Vlieger_, Jul 30 2017 *)
%Y A102642 Cf. A006530, A102640, A102641, A102643, A102644.
%K A102642 nonn
%O A102642 1,1
%A A102642 _Labos Elemer_, Jan 21 2005