This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087244 #28 Dec 29 2024 04:12:04 %S A087244 4,8,9,16,25,27,32,44,45,49,50,52,63,64,68,75,76,81,92,98,99,116,117, %T A087244 121,124,125,128,135,136,147,148,152,153,164,169,171,172,175,184,188, %U A087244 189,207,212,225,232,236,242,243,244,245,248,250,256,261,268,275,279 %N A087244 Nonsquarefree deficient numbers. %C A087244 The numbers of terms that do not exceed 10^k, for k = 1, 2, ..., are 3, 21, 197, 1982, 19913, 199871, 1995546, 19967891, 199695593, 1996670090, ... . Apparently, the asymptotic density of this sequence exists and equals 0.1996... . - _Amiram Eldar_, Dec 29 2024 %H A087244 Michael De Vlieger, <a href="/A087244/b087244.txt">Table of n, a(n) for n = 1..10000</a> %e A087244 m = 45 - 3*3*5 and sigma(45) = 78 < 2m = 90. %t A087244 Select[Range@ 280, And[! SquareFreeQ@ #, DivisorSigma[1, #] < 2 #] &] (* _Michael De Vlieger_, Mar 25 2017 *) %o A087244 (PARI) isok(n) = !issquarefree(n) && (sigma(n) < 2*n); \\ _Michel Marcus_, Dec 18 2013 %o A087244 (Python) %o A087244 from sympy import divisor_sigma %o A087244 from sympy.ntheory.factor_ import core %o A087244 print([n for n in range(1,301) if core(n) != n and divisor_sigma(n)<2*n]) # _Indranil Ghosh_, Mar 26 2017 %Y A087244 Intersection of A013929 and A005100. %Y A087244 Cf. A087245, A087246, A087247, A008683, A000203, A005117, A005101. %K A087244 nonn %O A087244 1,1 %A A087244 _Labos Elemer_, Sep 05 2003