A320048 - OEIS

%I #24 Oct 10 2018 20:04:43

%S 5,7,11,13,17,19,22,23,26,29,31,34,37,38,39,41,43,46,47,51,53,57,58,

%T 59,61,62,67,68,69,71,73,74,76,79,82,83,86,87,89,92,93,94,97,101,103,

%U 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 One half of composite numbers k with the property that the symmetric representation of sigma(k) has two parts.

%C Also, even numbers of A239929 divided by two.

%C First differs from A101550 at a(51). - _R. J. Mathar_, Oct 04 2018

%F a(n) = A244894(n)/2.

%e 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 .

%e .     _ _ _ _ _ _ 9

%e .    |_ _ _ _ _  |

%e .              | |_

%e .              |_ _|_

%e .                  | |_ _ 9

%e .                  |_ _  |

%e .                      | |

%e .                      | |

%e .                      | |

%e .                      | |

%e .                      |_|

%e .

%Y 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 nonn

%O 1,1

%A _Omar E. Pol_, Oct 04 2018