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A237352 a(1)=1; for n>1, a(n) is the smallest positive integer for which sigma(a(n)) is a proper multiple of sigma(a(n-1)).

%I A237352 #36 Sep 30 2014 06:55:20
%S A237352 1,2,5,6,14,30,66,138,210,462,930,1974,3810,6510,14322,26670,58674,
%T A237352 118110,245730,498666,826770,1720110,3784242,7617630,15728610,
%U A237352 27524910,53323410,110100270,218453970,480598734,853272210,1877198862,3413108370,6772073070
%N A237352 a(1)=1; for n>1, a(n) is the smallest positive integer for which sigma(a(n)) is a proper multiple of sigma(a(n-1)).
%C A237352 Subsequence of A090552.
%C A237352 The first term of A090552 that is not here is 11 since sigma(11) equals sigma(a(4)), so it is not a proper multiple.
%H A237352 Hiroaki Yamanouchi, <a href="/A237352/b237352.txt">Table of n, a(n) for n = 1..50</a>
%o A237352 (PARI) lista(nn) = {n = 1; precs = sigma(n); print1(n, ", "); for (n=2, nn, if ((((ns=sigma(n)) % precs) == 0) && (ns != precs), precs = ns; print1(n, ", ");););}
%Y A237352 Cf. A090552.
%K A237352 nonn
%O A237352 1,2
%A A237352 _Michel Marcus_, Apr 22 2014
%E A237352 a(33)-a(34) from _Hiroaki Yamanouchi_, Sep 30 2014