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 A227759 #7 Jul 23 2025 05:39:16 %S A227759 1,2,4,9,13,16,18,25,36,37,43,49,50,61,64,67,73,81,97,98,100,109,121, %T A227759 144,151,157,163,169,181,193,211,225,229,241,242,256,277,283,289,313, %U A227759 324,331,337,338,361,373,397,400,409,421,433,441,457,484,487,523,529 %N A227759 Numbers n such that A227758(n) = sigma(sigma(n)) - sigma(n) - n < 0, where sigma(n) = A000203(n) = sum of the divisors of n. %C A227759 Numbers n such that A051027(n) - A000203(n) - n < 0, where A000203(n) = sum of the divisors of n , A051027(n) = A000203(A000203(n)) = sigma(sigma(n)) = sum of the divisors of the sum of the divisors of n. %C A227759 Conjecture: a(n) = complement of union A000668 and A227760, where A000668 = Mersenne primes, A227760 = numbers n such that sigma(sigma(n)) - sigma(n) - n > 0. %F A227759 A227758(a(n)) < 0. %e A227759 Number 16 is in sequence because sigma(sigma(16)) - sigma(16) - 16 = 32 - 31 - 16 = -15 < 0. %Y A227759 Cf. A000203, A051027, A000668, A227760, A227758. %K A227759 nonn %O A227759 1,2 %A A227759 _Jaroslav Krizek_, Jul 29 2013