A175307 a(n) = the number of terms in row n of A175306.

2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 4, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1, 3, 1, 2, 1, 1, 1

Offset

1,1

Comments

a(2n) = 1, and a(3n)=1, for all positive integers n.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

A175307:=proc(n)
local R, last, k, P;
R:= n;
last:= n;
P:= n;
while igcd(last, 6)=1 do
  for k from last+1 do
    if igcd(k-1, P) = 1 and igcd(k, P) = 1 and igcd(k+1, P) =1 then
      R:= R, k; last:= k; P:= P*k; break
    fi
  od
od;
nops([R])
end proc:
map(A175307, [$1..100]); # Robert Israel, Feb 10 2017

Mathematica

row[n_] := Module[{R = {n}, last = n, k, P = n}, While[GCD[last, 6] == 1, For[k = last + 1, True, k++, If[GCD[k - 1, P] == 1 && GCD[k, P] == 1 && GCD[k + 1, P] == 1, AppendTo[R, k]; last = k; P = P k; Break[]]]]; R];
a[n_] := Length[row[n]];
Array[a, 100] (* Jean-François Alcover, Jul 25 2020, after Robert Israel *)

Crossrefs

Cf. A175306

Sequence in context: A276949 A205794 A241665 * A324825 A316557 A353381

Adjacent sequences: A175304 A175305 A175306 * A175308 A175309 A175310

Keyword

nonn

Author

Leroy Quet, Mar 26 2010

Status

approved