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 A206028 #49 May 08 2020 23:11:39
%S A206028 1,4,5,11,7,20,9,26,18,28,13,55,15,36,35,57,19,72,21,77,45,52,25,130,
%T A206028 38,60,58,99,31,140,33,120,65,76,63,198,39,84,75,182,43,180,45,143,
%U A206028 126,100,49,285,66,152,95,165,55,232,91,234,105,124,61,385,63,132,162,247,105,248
%N A206028 a(n) is the sum of distinct values of sigma(d) where d runs over the divisors of n and sigma = A000203.
%C A206028 Sequence is not the same as A007429: a(66) = 248, A007429(66) = 260. Number 66 is the smallest number with at least two divisors d with the same sigma(d); see A206030.
%C A206028 In A007429 all values of sigma(d) of the divisors d of n are included in the sum with repetitions allowed. In this sequence only the distinct values of sigma(d) of the divisors d of n are included in the sum.
%C A206028 If a term is a prime p when n = 2^j then p = 2^(j+2)-(j+3) is also a term of A099440 (primes of the form 2^n-n-1). Greater of twin primes are terms. - _Metin Sariyar_, Apr 03 2020
%H A206028 Andrew Howroyd, <a href="/A206028/b206028.txt">Table of n, a(n) for n = 1..10000</a>
%F A206028 a(p) = p+2, a(pq) = (p+2)*(q+2) for p, q = distinct primes.
%F A206028 a(n) = A184387(n) - A206029(n) = A000217(A000203(n)) - A206029(n).
%F A206028 a(2^n) = 2^(n+2) - (n+3). - _Metin Sariyar_, Apr 09 2020
%e A206028 For n=6 -> divisors d of 6: 1,2,3,6; corresponding values of sigma(d): 1,3,4,12; a(6) = Sum of k = 1+3+4+12 = 20.
%e A206028 For n=66 -> divisors d of 66: 1,2,3,6,11,22,33,66; corresponding values of sigma(d): 1,3,4,12,12,36,48,144; a(66) = Sum of k = 1+3+4+12+36+48+144 = 248 (note that only one twelve is added.).
%t A206028 Table[Total[Union[DivisorSigma[1, Divisors[n]]]], {n, 100}] (* _T. D. Noe_, Feb 10 2012 *)
%o A206028 (PARI) a(n)={vecsum(Set(apply(sigma, divisors(n))))} \\ _Andrew Howroyd_, Aug 01 2018
%Y A206028 Cf. A000203, A000217, A007429, A184387, A206029, A206030.
%K A206028 nonn
%O A206028 1,2
%A A206028 _Jaroslav Krizek_, Feb 03 2012
%E A206028 Name clarified by _David A. Corneth_, Aug 01 2018
%E A206028 a(62)-a(66) from _Andrew Howroyd_, Aug 01 2018