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A280919 Precipices from the successive terraces, descending by the main diagonal of the pyramid described in A245092. Also first differences of A071562. 10
1, 2, 2, 2, 1, 3, 3, 1, 2, 2, 4, 1, 3, 2, 2, 3, 1, 4, 2, 3, 3, 1, 1, 4, 2, 4, 3, 1, 2, 4, 2, 5, 3, 1, 3, 4, 2, 1, 5, 2, 1, 1, 4, 4, 2, 2, 5, 3, 1, 5, 2, 2, 2, 3, 5, 3, 1, 6, 3, 1, 2, 4, 2, 3, 3, 1, 1, 6, 4, 2, 5, 3, 2, 3, 1, 2, 2, 4, 4, 1, 1, 6, 4, 1, 3, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Descending by the main diagonal of the pyramid, A071562 gives the levels where we can find a terrace.

The terraces at the k-th level of the pyramid are also the parts of the symmetric representation of sigma(k).

a(n) is the length of the n-th vertical line segment at the main diagonal of the pyramid.

a(n) is the precipice of A071562(n).

The structure of the step pyramid arises after the 90-degree-zig-zag folding of the diagram of the isosceles triangle A237593.

The step pyramid is also one of the 3D-quadrants of the step pyramid described in A244050.

Equals nonzero terms of A259179. - Omar E. Pol, Apr 17 2018

LINKS

Robert Price, Table of n, a(n) for n = 1..13750

Omar E. Pol, Illustration of the isosceles triangle of A237593 (rows 1..28)

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

FORMULA

a(n) = A280223(A071562(n)).

MATHEMATICA

Differences@ Select[Range@ 228, Function[n, Total@ Select[Divisors@ n, Sqrt[n/2] <= # < Sqrt[2 n] &] != 0]] (* Michael De Vlieger, Jan 13 2017, after Robert G. Wilson v at A071562 *)

CROSSREFS

For more information about the precipices see A276112, A277437, A280223 and A280295.

Cf. A000203, A071562, A196020, A235791, A236104, A237048, A237591, A237593, A237270, A237271, A244050, A245092, A259179, A262626.

Sequence in context: A324100 A127953 A260418 * A209266 A269400 A130267

Adjacent sequences:  A280916 A280917 A280918 * A280920 A280921 A280922

KEYWORD

nonn

AUTHOR

Omar E. Pol, Jan 10 2017

EXTENSIONS

More terms from Michael De Vlieger, Jan 13 2017

STATUS

approved

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Last modified August 10 11:52 EDT 2020. Contains 336379 sequences. (Running on oeis4.)