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 A320048 #24 Oct 10 2018 20:04:43 %S A320048 5,7,11,13,17,19,22,23,26,29,31,34,37,38,39,41,43,46,47,51,53,57,58, %T A320048 59,61,62,67,68,69,71,73,74,76,79,82,83,86,87,89,92,93,94,97,101,103, %U A320048 106,107,109,111,113,116,118,122,123,124,127,129,131,134,137,139,141,142,146,148,149,151,157,158,159,163,164 %N A320048 One half of composite numbers k with the property that the symmetric representation of sigma(k) has two parts. %C A320048 Also, even numbers of A239929 divided by two. %C A320048 First differs from A101550 at a(51). - _R. J. Mathar_, Oct 04 2018 %F A320048 a(n) = A244894(n)/2. %e A320048 5 is in the sequence because 10 is a composite number, and the symmetric representation of sigma(10) = 18 has two parts (as shown below), and 10/2 = 5. %e A320048 . %e A320048 . _ _ _ _ _ _ 9 %e A320048 . |_ _ _ _ _ | %e A320048 . | |_ %e A320048 . |_ _|_ %e A320048 . | |_ _ 9 %e A320048 . |_ _ | %e A320048 . | | %e A320048 . | | %e A320048 . | | %e A320048 . | | %e A320048 . |_| %e A320048 . %Y A320048 Cf. A101550, A237271 (number of parts), A237270, A237593, A238443, A238524, A239929 (two parts), A239660, A239929, A239932, A239934, A240062 (k parts), A244894, A245092, A262626, A280107 (four parts). %K A320048 nonn %O A320048 1,1 %A A320048 _Omar E. Pol_, Oct 04 2018