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Numbers k such that bsigma(k) = bsigma(k+1), where bsigma(k) is the sum of the bi-unitary divisors of k (A188999).
26

%I #17 Jul 21 2021 22:49:29

%S 14,27,44,459,620,957,1334,1634,1652,2204,2685,3195,3451,3956,5547,

%T 8636,8907,9844,11515,11745,16874,19491,20145,20155,27643,31724,33998,

%U 38180,41265,41547,42818,45716,48364,64665,74875,74918,79316,79826,79833,83780,84134

%N Numbers k such that bsigma(k) = bsigma(k+1), where bsigma(k) is the sum of the bi-unitary divisors of k (A188999).

%H Amiram Eldar, <a href="/A293183/b293183.txt">Table of n, a(n) for n = 1..2148</a> (terms below 2*10^10)

%e 14 is in the sequence since bsigma(14) = bsigma(15) = 24.

%t f[n_] := Select[Divisors[n], Function[d, CoprimeQ[d, n/d]]]; bsigma[m_] :=

%t DivisorSum[m, # &, Last@Intersection[f@#, f[m/#]] == 1 &]; a = {}; b1 = 0; Do[b2 = bsigma[k]; If[b1 == b2, a = AppendTo[a, k - 1]]; b1 = b2, {k, 1, 10^6}]; a (* after _Michael De Vlieger_ at A188999 *)

%Y Cf. A002961, A064125, A188999.

%K nonn

%O 1,1

%A _Amiram Eldar_, Oct 01 2017