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A347937 Numbers k such that k and k+1 are both terms of A347935. 1

%I #18 Sep 26 2021 13:21:05

%S 2282175,16769024,18356624,27252224,32493824,35820224,46577024,

%T 50968575,51962624,53992575,55130624,61854975,63101024,63140175,

%U 69980624,72525375,73378304,74376224,80791424,82389824,98834175,102650624,105674624,107769375,109001024,110238975

%N Numbers k such that k and k+1 are both terms of A347935.

%H David A. Corneth, <a href="/A347937/b347937.txt">Table of n, a(n) for n = 1..2372</a> (first 103 terms from Amiram Eldar)

%e 2282175 is a term since A187795(2282175) = 4801650 > 2*2282175 = 4564350 and A187795(2282176) = 4630080 > 2*2282176 = 4564352.

%t abQ[n_] := DivisorSigma[1, n] > 2*n; s[n_] := DivisorSum[n, # &, abQ[#] &]; q[n_] := s[n] > 2*n; seq = {}; q1 = q[1]; Do[q2 = q[n]; If[q1 && q2, AppendTo[seq, n-1]]; q1 = q2, {n, 2, 2*10^7}]; seq

%o (PARI) isok1(k) = sumdiv(k, d, if (sigma(d)>2*d, d)) > 2*k; \\ A347935

%o isok(k) = isok1(k) && isok1(k+1); \\ _Michel Marcus_, Sep 20 2021

%Y Subsequence of A005101, A096399 and A347935.

%Y Cf. A187795, A347936, A347939.

%K nonn

%O 1,1

%A _Amiram Eldar_, Sep 20 2021

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Last modified June 12 10:07 EDT 2024. Contains 373329 sequences. (Running on oeis4.)