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%I #25 Aug 02 2024 14:17:20
%S 45,105,117,165,225,273,297,315,345,357,405,465,513,525,561,585,621,
%T 693,705,765,777,825,837,861,885,945,1005,1113,1125,1155,1185,1197,
%U 1281,1305,1365,1395,1425,1485,1521,1545,1575,1593,1617,1701,1725,1755,1785,1845
%N Odd numbers k such that sigma(k+1) < sigma(k).
%C Most terms are == 3 (mod 6), first term == 1 (mod 6) is a(130) = 5005. First term == 5 (mod 6) may be 247818996425. - _Jianing Song_, Apr 01 2018
%H Amiram Eldar, <a href="/A067828/b067828.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[1, 2000, 2], DivisorSigma[1, #] > DivisorSigma[1, # + 1] &] (* _Amiram Eldar_, Jun 06 2022 *)
%t Select[Flatten[Position[Partition[DivisorSigma[1,Range[2000]],2,1],_?(#[[2]]<#[[1]]&),1,Heads-> False]],OddQ] (* _Harvey P. Dale_, Aug 02 2024 *)
%o (PARI) isok(n) = (n % 2) && (sigma(n+1) < sigma(n)); \\ _Michel Marcus_, Nov 23 2013
%Y Cf. A000203, A053224, A067825.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Feb 08 2002
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