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 A247473 #37 Sep 08 2022 08:46:09 %S A247473 1,4,8,32,128,256,512,1024,4096,8192,16384,32768,65536,131072,262144, %T A247473 524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864, %U A247473 134217728,268435456,536870912,1073741824,2147483648,4294967296,8589934592,17179869184,34359738368 %N A247473 Numbers of the form 2^k (k>=0) that are a sum of divisors of n for some n. %C A247473 Set of values A094502(n) = sigma(A046528(n)) in increasing order. %C A247473 Complement of A094505 with respect to A000079 (powers of 2). %C A247473 Corresponding values of numbers k>0 are in A180221. %F A247473 a(1) = 1, for n>=2, a(n) = 2^A180221(n-1). %e A247473 32 = 2^5 is in sequence because there are numbers n = 21 and 31 with sigma(n) = 32. %o A247473 (Magma) Set(Sort([SumOfDivisors(n): n in [A046528(n)]])) %o A247473 (Magma) Set(Sort([SumOfDivisors(n): n in[1..10000], k in [0..100] | SumOfDivisors(n) eq 2^k])) %o A247473 (Magma) [1] cat [2^n: n in[A180221(n)]] %Y A247473 Cf. A000079, A000203, A046528, A078426, A094502, A094505, A180221. %K A247473 nonn %O A247473 1,2 %A A247473 _Jaroslav Krizek_, Feb 27 2015