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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. 11
 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 stepped pyramid arises after the 90-degree-zig-zag folding of the diagram of the isosceles triangle A237593. The stepped pyramid is also one of the 3D-quadrants of the stepped 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 A359930 A269400 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 February 21 12:33 EST 2024. Contains 370235 sequences. (Running on oeis4.)