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Numbers k such that sigma(k) = sigma(k + 15).
1

%I #21 Oct 29 2018 03:29:51

%S 26,62,20840574,25741470,60765690,102435795,277471467,361466454,

%T 464465910,1110512403,1927430490,2741174163,3631266639,3844534602,

%U 3982743750,4565968407,4612184562,4829319495,4981969978,7066794735,13484870399,14268004443,14550390855,15051147111

%N Numbers k such that sigma(k) = sigma(k + 15).

%H Giovanni Resta, <a href="/A321023/b321023.txt">Table of n, a(n) for n = 1..116</a> (terms < 2.5*10^12)

%e sigma(26) = sigma(41) = 42, sigma(62) = sigma(77) = 96.

%o (PARI) my(V=vector(15)); for(n=1, 2^28, my(s=sigma(n), r=(n%15)+1); if (s==V[r], print1(n-15, ", ")); V[r]=s)

%Y Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015882, A015883, A172335, A181647, A172333.

%K nonn

%O 1,1

%A _Tomohiro Yamada_, Oct 26 2018

%E a(7)-a(9) from _Amiram Eldar_, Oct 26 2018

%E a(10)-a(24) from _Giovanni Resta_, Oct 26 2018