cp's OEIS Frontend

A285890 The greater of the lexicographically least pair (x, y) such that 0 < x < y and sigma(x) = sigma(y) = n + x + y.

%I A285890 #19 May 15 2017 09:59:27
%S A285890 284,75,184,615,110,435,212,585,70,195,56,30429,1012,915,182,297,92,
%T A285890 16983,1886,1725,250,345,182,2415,716,2175,130,285,506,975,78,5145,
%U A285890 418,1107,225,1305,1504,9275,246,2001,1336,35875,2002,6405,322,915,176,7315,1292
%N A285890 The greater of the lexicographically least pair (x, y) such that 0 < x < y and sigma(x) = sigma(y) = n + x + y.
%H A285890 Paolo P. Lava, <a href="/A285890/b285890.txt">Table of n, a(n) for n = 0..1000</a>
%e A285890 a(3) = 615: sigma(615) = sigma(390) = 615 + 390 + 3 = 1008;
%e A285890 a(4) = 110: sigma(110) = sigma(102) = 110 + 102 + 4 = 216;
%e A285890 a(5) = 435: sigma(435) = sigma(280) = 435 + 280 + 5 = 720.
%p A285890 with(numtheory): P:=proc(q) local a,b,k,n; for n from 0 to q do for k from 1 to q do
%p A285890 a:=sigma(k)-k-n; b:=sigma(a)-a-n; if a>0 and b=k and a<>b then print(a); break;
%p A285890 fi; od; od; end: P(10^9);
%t A285890 Table[m = 1; While[MissingQ@ Set[k, SelectFirst[Range[m - 1], DivisorSigma[1, m] == DivisorSigma[1, #] == m + # + n &]], m++]; {k, m}, {n, 0, 10}][[All, -1]] (* Version 10.2, or *)
%t A285890 Do[m = 1; While[Set[k, Module[{k = 1}, While[! Xor[DivisorSigma[1, m] == DivisorSigma[1, k] == m + k + n, k >= m], k++]; k]] >= m, m++]; Print@ m, {n, 0, 10}] (* _Michael De Vlieger_, Apr 28 2017 *)
%Y A285890 Cf. A000203, A095702, A285889, A285892.
%K A285890 nonn,easy
%O A285890 0,1
%A A285890 _Paolo P. Lava_, Apr 28 2017