login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A233342 Rectangular array by antidiagonals: row n shows the numbers m for which n is the number of applications of the mapping r(k) = k - (greatest prime divisor or k) required to map m to 0. 3

%I #8 Dec 18 2013 23:36:19

%S 1,2,4,3,6,8,5,10,9,12,7,14,15,18,25,11,22,16,20,27,30,13,26,21,24,35,

%T 40,32,17,34,33,28,55,42,45,48,19,38,39,36,65,60,49,50,63,23,46,51,44,

%U 85,66,77,56,99,70,29,58,57,52,95,78,81,84,105,108,75

%N Rectangular array by antidiagonals: row n shows the numbers m for which n is the number of applications of the mapping r(k) = k - (greatest prime divisor or k) required to map m to 0.

%C Every positive integer occurs exactly once in the array, so that the sequence is a permutation of the natural numbers.

%C Row 1: A008578 (primes at the beginning of the 20th century)

%C Row 2: A100484 (even semiprimes)

%C Col 1: A233341

%H Clark Kimberling, <a href="/A233342/b233342.txt">Antidiagonals n = 1..60, flattened</a>

%e Northwest corner:

%e 1 ... 2 ... 3 ... 5 ... 7 ... 11 .. 13

%e 4 ... 6 ... 10 .. 14 .. 22 .. 26 .. 34

%e 8 ... 9 ... 15 .. 16 .. 21 .. 33 .. 39

%e 12 .. 18 .. 20 .. 24 .. 28 .. 36 .. 44

%e 25 .. 27 .. 35 .. 55 .. 65 .. 85 .. 95

%e 30 .. 40 .. 42 .. 60 .. 66 .. 78 .. 90

%t z = 40000; h[n_] := h[n] = n - FactorInteger[n][[-1, 1]]; t[n_] := Drop[FixedPointList[h, n], -2]; a = Table[Length[t[n]], {n, 1, z}] ; r[n_] := r[n] = Flatten[Position[a, n]]; w[n_, k_] := r[n][[k]]; TableForm[Table[w[n, k], {n, 1, 10}, {k, 1, 10}]]

%t u = Table[w[n - k + 1, k], {n, 14}, {k, n, 1, -1}] // Flatten

%Y Cf. A233341, A000040, A100484.

%K nonn,tabl,easy

%O 1,2

%A _Clark Kimberling_, Dec 07 2013

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)