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 A047931 #16 Apr 10 2018 08:28:07
%S A047931 0,1,2,2,2,2,3,2,2,3,2,3,2,3,2,3,2,3,3,2,3,2,3,3,2,3,3,2,3,3,2,3,3,2,
%T A047931 3,3,3,2,3,3,2,3,3,3,2,3,3,3,2,3,3,3,2,3,3,3,2,3,3,3,3,2,3,3,3,2,3,3,
%U A047931 3,3,2,3,3,3,3,2,3,3,3,3,2,3,3,3,3,2,3,3,3,3,3
%N A047931 Number of new penny-penny contacts when putting pennies on a table following a spiral pattern.
%H A047931 R. W. Grosse-Kunstleve, <a href="http://web.archive.org/web/20050425075654/http://cci.lbl.gov/~rwgk/EIS/PennySpiral.html">Penny Spiral Sequence</a>
%F A047931 The n-th "chunk" consists of 2 3{n-2} 2 3{n-1} 2 3{n-1} 2 3{n-1} 2 3{n-1} 2 3{n}, where a{b} symbolizes b repetitions of a.
%e A047931 From _Omar E. Pol_, Nov 16 2016: (Start)
%e A047931 The sequence written as a spiral begins:
%e A047931 .
%e A047931 . 2 - 3 - 3 - 3 - 3 - 2
%e A047931 . / \
%e A047931 . 3 2 - 3 - 3 - 3 - 2 3
%e A047931 . / / \ \
%e A047931 . 3 3 2 - 3 - 3 - 2 3 3
%e A047931 . / / / \ \ \
%e A047931 . 3 3 3 2 - 3 - 2 3 3 3
%e A047931 . / / / / \ \ \ \
%e A047931 . 3 3 3 3 2 - 2 3 3 3 3
%e A047931 . / / / / / \ \ \ \ \
%e A047931 . 2 2 2 2 2 0 - 1 2 2 2 2
%e A047931 . \ \ \ \ \ / / / /
%e A047931 . 3 3 3 3 2 - 3 - 2 3 3 3
%e A047931 . \ \ \ \ / / /
%e A047931 . 3 3 3 2 - 3 - 3 - 2 3 3
%e A047931 . \ \ \ / /
%e A047931 . 3 3 2 - 3 - 3 - 3 - 2 3
%e A047931 . \ \ /
%e A047931 . 3 2 - 3 - 3 - 3 - 3 - 2
%e A047931 . \
%e A047931 . 2 - 3 - 3 - 3 - 3 - 3
%e A047931 (End)
%Y A047931 Cf. A047932.
%K A047931 nonn
%O A047931 1,3
%A A047931 _Ralf W. Grosse-Kunstleve_