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 A319801 #18 Sep 28 2018 22:48:44 %S A319801 3,5,7,11,13,17,19,21,23,27,29,31,33,37,39,41,43,47,51,53,55,57,59,61, %T A319801 65,67,69,71,73,75,79,83,85,87,89,93,95,97,101,103,105,107,109,111, %U A319801 113,115,119,123,125,127,129,131,133,137,139,141,145,147,149,151,155,157,159,161,163,167,171,173,175,177 %N A319801 Odd numbers without middle divisors. %C A319801 Odd numbers k such that the symmetric representation of sigma(k) has an even number of parts. %C A319801 All odd primes (A065091) are in the sequence. %C A319801 For the definition of middle divisors, see A067742. %C A319801 For more information about the symmetric representation of sigma(k) see A237593. %e A319801 21 is in the sequence because it's an odd number and the symmetric representation of sigma(21) = 32 has an even number of parts (more exactly four parts), as shown below: %e A319801 . _ _ _ _ _ _ _ _ _ _ _ 11 %e A319801 . |_ _ _ _ _ _ _ _ _ _ _| %e A319801 . | %e A319801 . | %e A319801 . |_ _ _ 5 %e A319801 . |_ _ |_ %e A319801 . |_ _|_ %e A319801 . | |_ 5 %e A319801 . |_ | %e A319801 . | | %e A319801 . |_|_ _ _ _ 11 %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . | | %e A319801 . |_| %e A319801 . %Y A319801 Intersection of A005408 and A071561. %Y A319801 Cf. A000203, A065091, A067742, A071090, A071562, A236104, A237270, A237271, A237593, A239931, A239933, A240542, A245092, A280919, A281007, A296508, A299761, A299777, A303297, A319529, A319796, A319802. %K A319801 nonn %O A319801 1,1 %A A319801 _Omar E. Pol_, Sep 28 2018