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A325300
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a(n) is the number of faces of the stepped pyramid with n levels described in A245092.
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3
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6, 9, 15, 20, 24, 31, 35, 42, 49, 59, 63, 72, 76, 84, 95, 106, 110, 121, 125
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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Table of n, a(n) for n=1..19.
Omar E. Pol, Perspective view of the pyramid (first 16 levels)
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FORMULA
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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).
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EXAMPLE
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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.
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CROSSREFS
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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
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KEYWORD
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nonn,more
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AUTHOR
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Omar E. Pol, Apr 16 2019
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STATUS
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approved
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