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URL: https://oeis.org/A325300

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A325300
a(n) is the number of faces of the stepped pyramid with n levels described in A245092.
5
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.
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).
Sequence in context: A316035 A316036 A316037 * A316038 A316039 A316040
KEYWORD
nonn,more
AUTHOR
Omar E. Pol, Apr 16 2019
STATUS
approved