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 A325300 #18 Dec 31 2020 11:11:15 %S A325300 6,9,15,20,24,31,35,42,49,59,63,72,76,84,95,106,110,121,125 %N A325300 a(n) is the number of faces of the stepped pyramid with n levels described in A245092. %C A325300 To calculate a(n) consider that levels greater than n do not exist. %C A325300 The shape of the n-th level of the pyramid allows us to know if n is prime (see the Formula section). %C A325300 For more information about the sequences that we can see in the pyramid see A262626. %H A325300 Omar E. Pol, <a href="http://www.polprimos.com/imagenespub/polpyr05.jpg">Perspective view of the pyramid (first 16 levels)</a> %F A325300 a(n) = A325301(n) - A325302(n) + 2 (Euler's formula). %F A325300 a(n) = A323645(n) + 3. %F A325300 a(n) = a(n-1) + 4 iff n is a prime > 3 (A215848). %e A325300 For n = 1 the first level of the stepped pyramid (starting from the top) is a cube, and a cube has six faces, so a(1) = 6. %Y A325300 Cf. A325301 (number of edges), A325302 (number of vertices). %Y A325300 Cf. A196020, A215848, A235791, A236104, A237270, A237271, A237591, A237593, A245092, A262626, A299692, A323645, A323648. %K A325300 nonn,more %O A325300 1,1 %A A325300 _Omar E. Pol_, Apr 16 2019