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

%I A192489 #16 Mar 10 2019 21:40:44
%S A192489 2,3,5,7,11,13,17,19,23,25,29,31,35,37,41,43,47,49,53,55,59,61,67,71,
%T A192489 73,77,79,83,85,89,91,95,97,101,103,107,109,113,115,119,121,127,131,
%U A192489 133,137,139,143,145,149,151,155,157,161,163,167,169,173,175,179
%N A192489 Numbers m such that A099427(m) = 2.
%C A192489 A099427(a(n)) = 2;
%C A192489 primes and squares of primes greater than 9 are subsequences, cf. A000040, A001248, A000430;
%C A192489 GCD(A099427(a(n)-1), A099427(a(n))) = 1;
%C A192489 a(n) = A038179(n) for n <= 22.
%C A192489 The next term divisible by 3 is a(137)=429. - _Joe Slater_, Jan 10 2017
%C A192489 All terms after the first are odd, since A099427(n) == n+1 (mod 2) for n >= 3. - _Robert Israel_, Jan 10 2017
%H A192489 Reinhard Zumkeller, <a href="/A192489/b192489.txt">Table of n, a(n) for n = 1..10000</a>
%p A192489 A099427:= proc(n) option remember; 1 + igcd(n,procname(n-1)) end proc:
%p A192489 A099427(1):= 1:
%p A192489 select(A099427=2, [$1..1000]); # _Robert Israel_, Jan 10 2017
%t A192489 (* b = A099427 *) b[1] = 1; b[n_] := b[n] = GCD[n, b[n - 1]] + 1;
%t A192489 Select[Range[200], b[#] == 2&] (* _Jean-François Alcover_, Mar 10 2019 *)
%o A192489 (Haskell)
%o A192489 a192489 n = a192489_list !! (n-1)
%o A192489 a192489_list = f 2 1 where
%o A192489    f n x | x' == 2   = n : f (n+1) x'
%o A192489          | otherwise = f (n+1) x'
%o A192489          where x' = 1 + gcd n x
%K A192489 nonn
%O A192489 1,1
%A A192489 _Reinhard Zumkeller_, Jul 02 2011