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A317304 Numbers k with the property that both Dyck paths of the symmetric representation of sigma(k) have a central valley. 5
4, 5, 11, 12, 13, 14, 22, 23, 24, 25, 26, 27, 37, 38, 39, 40, 41, 42, 43, 44, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also triangle read by rows which gives the even-indexed rows of triangle A014132.

There are no triangular number (A000217) in this sequence.

For more information about the symmetric representation of sigma see A237593 and its related sequences.

Equivalently, numbers k with the property that both Dyck paths of the symmetric representation of sigma(k) have an even number of peaks. - Omar E. Pol, Sep 13 2018

LINKS

Table of n, a(n) for n=1..69.

EXAMPLE

Written as an irregular triangle in which the row lengths are the positive even numbers, the sequence begins:

    4,   5;

   11,  12,  13,  14;

   22,  23,  24,  25,  26,  27;

   37,  38,  39,  40,  41,  42,  43,  44;

   56,  57,  58,  59,  60,  61,  62,  63,  64,  65;

   79,  80,  81,  82,  83,  84,  85,  86,  87,  88,  89,  90;

  106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119;

...

Illustration of initial terms:

-------------------------------------------------

   k  sigma(k)  Diagram of the symmetry of sigma

-------------------------------------------------

                       _ _           _ _ _ _

                      | | |         | | | | |

                     _| | |         | | | | |

                 _ _|  _|_|         | | | | |

   4      7     |_ _ _|             | | | | |

   5      6     |_ _ _|             | | | | |

                                 _ _|_| | | |

                               _|    _ _|_| |

                             _|     |  _ _ _|

                            |      _|_|

                 _ _ _ _ _ _|  _ _|

  11     12     |_ _ _ _ _ _| |  _|

  12     28     |_ _ _ _ _ _ _| |

  13     14     |_ _ _ _ _ _ _| |

  14     24     |_ _ _ _ _ _ _ _|

.

For the first six terms of the sequence we can see in the above diagram that both Dyck path (the smallest and the largest) of the symmetric representation of sigma(k) have a central valley.

Compare with A317303.

CROSSREFS

Row sums give A084367. n >= 1.

Column 1 gives A084849, n >= 1.

Column 2 gives A096376, n >= 1.

Right border gives the nonzero terms of A014106.

The union of A000217, A317303 and this sequence gives A001477.

Some other sequences related to the central peak or the central valley of the symmetric representation of sigma are A000217, A000384, A007606, A007607, A014105, A014132, A162917, A161983, A317303. See also A317306.

Cf. A000203, A005843, A196020, A236104, A235791, A237048, A237591, A237593, A237270, A237271, A239660, A239931, A239932, A239933, A239934, A244050, A245092, A249351, A262626.

Sequence in context: A064945 A069820 A318446 * A178823 A188053 A261673

Adjacent sequences:  A317301 A317302 A317303 * A317305 A317306 A317307

KEYWORD

nonn,tabf

AUTHOR

Omar E. Pol, Aug 27 2018

STATUS

approved

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Last modified February 16 12:48 EST 2019. Contains 320163 sequences. (Running on oeis4.)