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A328327 Numbers k such that both k and k+1 are Zumkeller numbers (A083207). 3
5984, 7424, 21735, 21944, 26144, 27404, 39375, 43064, 49664, 56924, 58695, 61424, 69615, 70784, 76544, 77175, 79695, 81080, 81675, 82004, 84524, 84644, 89775, 91664, 98175, 103455, 104895, 106784, 109395, 111824, 116655, 116864, 120015, 121904, 122264, 126224 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms k such that both k and k+1 are primitive Zumkeller numbers (A180332) are 82004, 84524, 158235, 516704, 2921535, 5801984, ...

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..5000

MATHEMATICA

zumkellerQ[n_] := Module[{d = Divisors[n], t, ds, x}, ds = Plus @@ d; If[Mod[ds, 2] > 0, False, t = CoefficientList[Product[1 + x^i, {i, d}], x]; t[[1 + ds/2]] > 0]]; zq1 = False; s = {}; Do[zq2 = zumkellerQ[n]; If[zq1 && zq2, AppendTo[s, n - 1]]; zq1 = zq2, {n, 2, 10^5}]; s (* after T. D. Noe at A083207 *)

CROSSREFS

Cf. A083207, A180332.

Subsequence of A096399.

Sequence in context: A157666 A176374 A282191 * A237011 A274362 A233871

Adjacent sequences:  A328324 A328325 A328326 * A328328 A328329 A328330

KEYWORD

nonn

AUTHOR

Amiram Eldar, Oct 12 2019

STATUS

approved

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Last modified October 16 03:52 EDT 2021. Contains 348035 sequences. (Running on oeis4.)