|
%I #18 Jun 03 2019 03:01:59
%S 2,3,5,6,7,11,13,17,19,23,28,29,31,37,41,43,47,53,59,61,67,71,73,79,
%T 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,
%U 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271
%N Numbers which are an integral multiple of the sum of their proper divisors: prime and perfect numbers.
%C Note that numbers which are an integral multiple of the sum of their proper divisors excluding 1 (A048050) are the squares of primes (A001248).
%C Subsequence of A166070. - _Jaroslav Krizek_, Oct 06 2009
%p isA053813 := proc(n) add(1/j, j=numtheory:-divisors(n)): numer(%) = denom(%) + 1 end: select(isA053813, [$1..271]); # _Peter Luschny_, Oct 03 2018
%t Select[Range[300], PrimeQ[#] || DivisorSigma[1, #] == 2*#&] (* _Jean-François Alcover_, Jun 03 2019 *)
%Y Cf. A000040, A000396, A001065.
%Y Cf. A048050, A001248.
%Y Cf. A166070.
%K nonn
%O 1,1
%A _Henry Bottomley_, Mar 28 2000
|
