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 A027388 #27 Jul 16 2025 22:30:36
%S A027388 0,2,2,2,2,2,1,4,0,1,2,4,4,4,4,4,3,6,2,3,2,4,4,4,4,4,3,6,2,3,2,4,4,4,
%T A027388 4,4,3,6,2,3,2,4,4,4,4,4,3,6,2,3,2,4,4,4,4,4,3,6,2,3,1,3,3,3,3,3,2,5,
%U A027388 1,2,4,6,6,6,6,6,5,8,4,5,0
%N A027388 Write digits for n, count endpoints (version 3).
%C A027388 Number of endpoints: 0,8 - zero, 6,9 - one, 1,2,3,4,5 - two, 7 - four. - _Michael B. Porter_, Oct 28 2017
%H A027388 Paolo Xausa, <a href="/A027388/b027388.txt">Table of n, a(n) for n = 0..10000</a>
%F A027388 a(10*n + d) = a(n) + e where e is the number of endpoints of single digit d. - _David A. Corneth_, Oct 28 2017
%e A027388 The digit 1 has two endpoints, and the digit 8 has no endpoints, so a(18) = 2. - _Michael B. Porter_, Oct 28 2017
%t A027388 A027388[n_] := Total[Map[{0, 2, 2, 2, 2, 2, 1, 4, 0, 1}[[#+1]] &, IntegerDigits[n]]];
%t A027388 Array[A027388, 100, 0] (* _Paolo Xausa_, Jul 16 2025 *)
%o A027388 (PARI) a(n)=vecsum(apply(d->[0, 2, 2, 2, 2, 2, 1, 4, 0, 1][d+1], digits(n))); \\ based on program for A027386 by _Andrew Howroyd_, _Michael B. Porter_, Oct 28 2017
%Y A027388 Cf. A027386, A027387, A027389, A055642, A100910, A102683, A268643.
%K A027388 nonn,base
%O A027388 0,2
%A A027388 _N. J. A. Sloane_
%E A027388 a(6) corrected by _Michael B. Porter_, Oct 28 2017 (per _Andrew Howroyd_)
%E A027388 a(27) to a(80) by _Michael B. Porter_, Oct 28 2017