A192489 Numbers m such that A099427(m) = 2.

2, 3, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 35, 37, 41, 43, 47, 49, 53, 55, 59, 61, 67, 71, 73, 77, 79, 83, 85, 89, 91, 95, 97, 101, 103, 107, 109, 113, 115, 119, 121, 127, 131, 133, 137, 139, 143, 145, 149, 151, 155, 157, 161, 163, 167, 169, 173, 175, 179

Offset: 1

Author

Reinhard Zumkeller, Jul 02 2011

Keywords

• nonn

Comments

A099427(a(n)) = 2;

primes and squares of primes greater than 9 are subsequences, cf. A000040, A001248, A000430;

GCD(A099427(a(n)-1), A099427(a(n))) = 1;

a(n) = A038179(n) for n <= 22.

The next term divisible by 3 is a(137)=429. - Joe Slater, Jan 10 2017

All terms after the first are odd, since A099427(n) == n+1 (mod 2) for n >= 3. - Robert Israel, Jan 10 2017

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Programs

Haskell

a192489 n = a192489_list !! (n-1)
a192489_list = f 2 1 where
   f n x | x' == 2   = n : f (n+1) x'
         | otherwise = f (n+1) x'
         where x' = 1 + gcd n x

Maple

A099427:= proc(n) option remember; 1 + igcd(n,procname(n-1)) end proc:
A099427(1):= 1:
select(A099427=2, [$1..1000]); # Robert Israel, Jan 10 2017

Mathematica

(* b = A099427 *) b[1] = 1; b[n_] := b[n] = GCD[n, b[n - 1]] + 1;
Select[Range[200], b[#] == 2&] (* Jean-François Alcover, Mar 10 2019 *)