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 A251820 Numbers n for which the symmetric representation of sigma(n) has at least 3 parts, all having the same area. 2
 15, 5950 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(3) > 36000000. Also intersection of A241558 and A241559 (minimum = maximum) minus the union of A238443 and A239929 (number of parts <= 2). LINKS EXAMPLE The parts of the symmetric representations of sigma(15) and sigma(5950) are {8, 8, 8} and {4464, 4464, 4464}, respectively, so a(1) = 15 and a(2) = 5950. From Omar E. Pol, Dec 09 2014: (Start) Illustration of the symmetric representation of sigma(15) = 8 + 8 + 8 = 24 in the first quadrant: . .  _ _ _ _ _ _ _ _ 8 . |_ _ _ _ _ _ _ _| .                 | .                 |_ _ .                 |_  |_ 8 .                   |   |_ .                   |_ _  | .                       |_|_ _ _ 8 .                             | | .                             | | .                             | | .                             | | .                             | | .                             | | .                             | | .                             |_| . The three parts have the same area. (End) MATHEMATICA (* T[], row[], cD[] & tD[] are defined in A239663 *) a251820[n_] := Module[{pT = T[n, 1], cT, cL, cW = 0, cR = 0, sects = {}, j = 1, r = row[n], test = True}, While[test && j <= r, cT = T[n, j+1]; cL = pT - cT; cW += (-1)^(j+1) * tD[n, j]; If[cW == 0 && cR != 0, AppendTo[sects, cR]; cR = 0; If[Min[sects] != Max[sects], test = False], cR += cL * cW]; pT = cT; j++]; If[cW != 0, AppendTo[sects, 2 * cR - cW]]; Min[sects] == Max[sects] && Length[sects] > 1] Select[Range, a251820] (* data *) CROSSREFS Cf. A000203, A237593, A237270, A238443, A239663, A241558, A241559. Sequence in context: A249966 A167823 A199099 * A296177 A206360 A292972 Adjacent sequences:  A251817 A251818 A251819 * A251821 A251822 A251823 KEYWORD nonn,more,hard,bref AUTHOR Hartmut F. W. Hoft, Dec 09 2014 STATUS approved

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Last modified September 25 12:16 EDT 2021. Contains 347654 sequences. (Running on oeis4.)