A335442 List enumerated in lexicographic order of (n, s, k), where for each n >= 1, for each s a subset of 1..n with n-1 elements, and for each k in 0..n-1, we give the value of (Sum_{t subset of s, Card(t)=k} Product_{x in t} x).

1, 1, 1, 1, 2, 1, 3, 2, 1, 4, 3, 1, 5, 6, 1, 6, 11, 6, 1, 7, 14, 8, 1, 8, 19, 12, 1, 9, 26, 24, 1, 10, 35, 50, 24, 1, 11, 41, 61, 30, 1, 12, 49, 78, 40, 1, 13, 59, 107, 60, 1, 14, 71, 154, 120, 1, 15, 85, 225, 274, 120, 1, 16, 95, 260, 324, 144, 1, 17, 107, 307, 396, 180, 1, 18, 121, 372, 508, 240, 1, 19, 137, 461, 702, 360, 1, 20, 155, 580, 1044, 720

Offset

1,5

Comments

This sequence can be viewed as a triangle made of square blocks of increasing sizes: 1 X 1, 2 X 2, and so on. In block number n >= 1, the bottom-right corner is n!, the top-right one (n-1)!. The first row of block number n, which is row number binomial(n, 2) if we number the rows according to their second value, is the list of the unsigned Stirling numbers of the first kind, reversed. The subsequence {last element of row n} is A077012.

Block number n crops up for instance when studying -log(1-r), where r = e^(i*2*Pi/n); this is Sum_{K>=1} r^K/K = Sum_{K>=0} Sum_{L=1..n} r^L/(nK+L);

the term for K in the first sum, if put in the same denominator and if no simplification is carried out, has a numerator which is a combination of all (nK)^I * r^J; their coefficients are precisely the elements of block number n.

Links

Table of n, a(n) for n=1..91.

Luc Rousseau, Program for the computation of A335442 (SWI-Prolog)

Example

Table begins:
  +---+
  | 1 |
  +---+----+
  | 1    1 |
  | 1    2 |
  +--------+----+
  | 1    3    2 |
  | 1    4    3 |
  | 1    5    6 |
  +-------------+----+
  | 1    6   11    6 |
  | 1    7   14    8 |
  | 1    8   19   12 |
  | 1    9   26   24 |
  +------------------+----+
  | 1   10   35   50   24 |
  | 1   11   41   61   30 |
  | 1   12   49   78   40 |
  | 1   13   59  107   60 |
  | 1   14   71  154  120 |
  +-----------------------+----+
  | 1   15   85  225  274  120 |
  | 1   16   95  260  324  144 |
  | 1   17  107  307  396  180 |
  | 1   18  121  372  508  240 |
  | 1   19  137  461  702  360 |
  | 1   20  155  580 1044  720 |
  +----------------------------+----+
  | 1   21  175  735 1624 1764  720 |
  | 1   22  190  820 1849 2038  840 |
  | 1   23  207  925 2144 2412 1008 |
  | 1   24  226 1056 2545 2952 1260 |
  | 1   25  247 1219 3112 3796 1680 |
  | 1   26  270 1420 3929 5274 2520 |
  | 1   27  295 1665 5104 8028 5040 |
  +---------------------------------+----+
  etc.

Prog

(SWI-Prolog) See link.

Crossrefs

Cf. A000142, A008275, A077012.

Sequence in context: A141672 A141671 A309596 * A226247 A233742 A194856

Adjacent sequences: A335439 A335440 A335441 * A335443 A335444 A335445

Keyword

nonn,tabf

Author

Luc Rousseau, Jun 10 2020

Status

approved