A325300 a(n) is the number of faces of the stepped pyramid with n levels described in A245092.

6, 9, 15, 20, 24, 31, 35, 42, 49, 59, 63, 72, 76, 84, 95, 106, 110, 121, 125

Offset

1,1

Comments

To calculate a(n) consider that levels greater than n do not exist.

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

For more information about the sequences that we can see in the pyramid see A262626.

Links

Table of n, a(n) for n=1..19.

Omar E. Pol, Perspective view of the pyramid (first 16 levels)

Formula

a(n) = A325301(n) - A325302(n) + 2 (Euler's formula).

a(n) = A323645(n) + 3.

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

Example

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.

Crossrefs

Cf. A325301 (number of edges), A325302 (number of vertices).

Cf. A196020, A215848, A235791, A236104, A237270, A237271, A237591, A237593, A245092, A262626, A299692, A323645, A323648.

Sequence in context: A316035 A316036 A316037 * A316038 A316039 A316040

Adjacent sequences: A325297 A325298 A325299 * A325301 A325302 A325303

Keyword

nonn,more

Author

Omar E. Pol, Apr 16 2019

Status

approved