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 A334022 Numbers k such that s(k) = s(k+1) = s(k+2) = s(k+3), where s(k) is the sum of unitary divisors of k that are smaller than sqrt(k) (A334019). 0

%I #4 Apr 12 2020 21:44:03

%S 2,46351754,102841142,158071592,667930085,851043553,1097409992,

%T 1580045430,1595193655,1698842487,1919035496,1951958341,2279249234,

%U 2507918727,2520080695,2741951910,3335769314,3654512455,3713106152,4209598844,4351540982,4369408604,4480814965

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

%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]; s3 = s[3]; Do[s4 = s[n]; If[s1 == s2 && s2 == s3 && s3 == s4, AppendTo[seq, n - 3]]; s1 = s2; s2 = s3; s3 = s4, {n, 4, 10^9}]; seq

%Y Cf. A325175, A334019, A334020, A334021.

%K nonn

%O 1,1

%A _Amiram Eldar_, Apr 12 2020

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Last modified August 7 07:35 EDT 2024. Contains 375008 sequences. (Running on oeis4.)