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 A053813 #18 Jun 03 2019 03:01:59 %S A053813 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 A053813 83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173, %U A053813 179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271 %N A053813 Numbers which are an integral multiple of the sum of their proper divisors: prime and perfect numbers. %C A053813 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 A053813 Subsequence of A166070. - _Jaroslav Krizek_, Oct 06 2009 %p A053813 isA053813 := proc(n) add(1/j, j=numtheory:-divisors(n)): numer(%) = denom(%) + 1 end: select(isA053813, [$1..271]); # _Peter Luschny_, Oct 03 2018 %t A053813 Select[Range[300], PrimeQ[#] || DivisorSigma[1, #] == 2*#&] (* _Jean-François Alcover_, Jun 03 2019 *) %Y A053813 Cf. A000040, A000396, A001065. %Y A053813 Cf. A048050, A001248. %Y A053813 Cf. A166070. %K A053813 nonn %O A053813 1,1 %A A053813 _Henry Bottomley_, Mar 28 2000