A075033 - OEIS

%I #23 Jul 10 2020 14:09:17

%S 1,13,25,33,37,61,73,85,93,97,121,133,141,145,157,187,193,201,205,213,

%T 217,229,241,242,243,253,277,283,301,361,373,393,397,421,427,445,453,

%U 457,481,537,541,547,603,613,633,661,662,663,697,723,733,745,757,781

%N Numbers n such that tau(n) <= tau(n+1) <= tau(n+2) <= tau(n+3) where tau(n) = number of divisors of n.

%H Karl V. Keller, Jr., <a href="/A075033/b075033.txt">Table of n, a(n) for n = 1..10000</a>

%t With[{s = Partition[Differences@ Array[DivisorSigma[0, #] &, 800], 3, 1]}, Position[s, _?(AllTrue[#, # >= 0 &] &), {1}, Heads -> False][[All, 1]]] (* _Michael De Vlieger_, Jun 28 2020 *)

%o (Python)

%o from sympy import divisor_count as tau

%o [n for n in range(1, 801) if tau(n) <= tau(n+1) <= tau(n+2) <= tau(n+3)] # _Karl V. Keller, Jr._, Jul 10 2020

%Y Cf. A000005, A075032, A075034, A075035.

%K nonn

%O 1,2

%A _Amarnath Murthy_, Sep 02 2002

%E Added missing term and a(11)-a(54) from _Donovan Johnson_, Jun 15 2009