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A325300 a(n) is the number of faces of the stepped pyramid with n levels described in A245092. 3
6, 9, 15, 20, 24, 31, 35, 42, 49, 59, 63, 72, 76, 84, 95, 106, 110, 121, 125 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 24 13:13 EST 2021. Contains 341569 sequences. (Running on oeis4.)