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 A323645 #36 Dec 31 2020 11:11:15 %S A323645 3,6,12,17,21,28,32,39,46,56,60,69,73,81,92,103,107,118,122 %N A323645 a(n) is the number of visible faces in the perspective view of the stepped pyramid with n levels described in A245092. %C A323645 The shape of the n-th level of the pyramid allows us to know if n is prime (see the Formula section). %C A323645 For more sequences that we can find in the pyramid see A262626. %H A323645 Omar E. Pol, <a href="http://www.polprimos.com/imagenespub/polpyr05.jpg">Perspective view of the stepped pyramid (levels: 1..16) and A000203</a> %F A323645 a(n) = a(n-1) + 4 iff n is a prime > 3 (A215848). %F A323645 a(n) = A325300(n) - 3. - _Omar E. Pol_, Apr 17 2019 %Y A323645 Cf. A000040, A000203, A024916, A196020, A215848, A224880, A235791, A236104, A237048, A237270, A237271, A237593, A245092, A262626, A299692 (total area). %K A323645 nonn,more %O A323645 1,1 %A A323645 _Omar E. Pol_, Mar 20 2019 %E A323645 a(18)-a(19) from _Omar E. Pol_, Apr 18 2019