A323645 - OEIS

%I #36 Dec 31 2020 11:11:15

%S 3,6,12,17,21,28,32,39,46,56,60,69,73,81,92,103,107,118,122

%N a(n) is the number of visible faces in the perspective view of the stepped pyramid with n levels described in A245092.

%C The shape of the n-th level of the pyramid allows us to know if n is prime (see the Formula section).

%C For more sequences that we can find in the pyramid see A262626.

%H 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 a(n) = a(n-1) + 4 iff n is a prime > 3 (A215848).

%F a(n) = A325300(n) - 3. - _Omar E. Pol_, Apr 17 2019

%Y Cf. A000040, A000203, A024916, A196020, A215848, A224880, A235791, A236104, A237048, A237270, A237271, A237593, A245092, A262626, A299692 (total area).

%K nonn,more

%O 1,1

%A _Omar E. Pol_, Mar 20 2019

%E a(18)-a(19) from _Omar E. Pol_, Apr 18 2019