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%I #38 Apr 19 2022 04:59:25
%S 1,2,3,4,5,6,7,8,9,10,11,13,14,15,17,19,21,22,23,25,26,27,29,31,33,34,
%T 35,37,38,39,41,43,46,47,49,51,53,55,57,58,59,61,62,65,67,69,71,73,74,
%U 77,79,82,83,85,86,87,89,91,93,94,95,97,101,103,106
%N Numbers k such that product of proper divisors of k is <= k; i.e., product of divisors of k is <= k^2.
%C Numbers which are the product of up to two primes (not necessarily distinct) or the cube of a prime. Alternatively, numbers having prime decomposition p*q, where q either is distinct from p or equals p^k for 0 <= k <= 2.
%C Corresponds to numbers having at most four divisors. (For numbers with exactly four divisors see A030513.) - _Lekraj Beedassy_, Sep 23 2003
%C For n > 3: numbers that can occur as fourth divisors; union of A000040, A001248, A006881 and A030078. - _Reinhard Zumkeller_, May 15 2006
%D Liu Hongyan and Zhang Wenpeng, On the simple numbers and the mean value properties, Smarandache Notions (Book Series, Vol. 14), American Research Press, 2004; pp. 171-175.
%H Amiram Eldar, <a href="/A007964/b007964.txt">Table of n, a(n) for n = 1..10000</a>
%H F. Smarandache, <a href="http://www.gallup.unm.edu/~smarandache/OPNS.pdf">Only Problems, Not Solutions!</a> (listing the sequence as the "simple numbers" in Unsolved Problem: 23 p.23).
%t Select[Range[100], DivisorSigma[0, #] < 5 &] (* _Amiram Eldar_, Apr 30 2020 *)
%o (PARI) is(n)=numdiv(n)<5 \\ _Charles R Greathouse IV_, Sep 16 2015
%Y Cf. A007955, A058080.
%K nonn,easy
%O 1,2
%A R. Muller
%E Description corrected by _Henry Bottomley_, Nov 24 2000