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%I #61 Aug 01 2023 10:55:53
%S 1,13,61,73,133,145,193,205,253,397,457,481,493,553,565,613,625,661,
%T 673,733,757,793,817,853,913,973,997,1033,1093,1213,1237,1285,1321,
%U 1333,1453,1513,1537,1633,1645,1657,1681,1813,1825,1873,1933,2077,2113,2173,2233,2245,2293,2413,2497
%N Integers k such that sigma(k) <= sigma(k+1) <= sigma(k+2) <= sigma(k+3), where sigma is the sum of divisors.
%H Seiichi Manyama, <a href="/A359666/b359666.txt">Table of n, a(n) for n = 1..10000</a>
%e 73 is a term because sigma(73)=74 <= sigma(74)=114 <= sigma(75)=124 <= sigma(76)=140.
%t Position[OrderedQ /@ Partition[DivisorSigma[1, Range[2500]], 4, 1], True] // Flatten (* _Amiram Eldar_, Feb 28 2023 *)
%o (PARI) isok(n)=sigma(n)<=sigma(n+1) && sigma(n+1)<=sigma(n+2) && sigma(n+2)<=sigma(n+3)
%Y Cf. A000203, A053224, A323726, A364662.
%K nonn,easy
%O 1,2
%A _Alexandru Petrescu_, Feb 28 2023