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Numbers k such that s(k) = s(k+1) = s(k+2), where s(k) is the sum of unitary divisors of k that are smaller than sqrt(k) (A334019).
3

%I #8 Apr 13 2020 05:44:57

%S 2,3,7,1420,2505,11860,64060,64485,113413,158020,205365,332658,465272,

%T 522764,611085,614538,635053,664033,748484,771138,839213,881565,

%U 1011793,1090788,1190685,1248645,1306605,1488088,1607367,1613190,1836018,1884914,1911940,2286913

%N Numbers k such that s(k) = s(k+1) = s(k+2), where s(k) is the sum of unitary divisors of k that are smaller than sqrt(k) (A334019).

%H Amiram Eldar, <a href="/A334021/b334021.txt">Table of n, a(n) for n = 1..1000</a>

%e 2 is a term since A334019(2) = A334019(3) = A334019(4) = 1.

%t s[n_] := DivisorSum[n, # &, #^2 < n && CoprimeQ[#, n/#] &]; seq={}; s1 = s[1]; s2 = s[2]; Do[s3 = s[n]; If[s1 == s2 && s2 == s3, AppendTo[seq, n - 2]]; s1 = s2; s2 = s3, {n, 3, 10^5}]; seq

%Y Cf. A324310, A334019, A334020.

%K nonn

%O 1,1

%A _Amiram Eldar_, Apr 12 2020