OFFSET
1,4
COMMENTS
It would be nice to have an alternative description of this sequence, one that is not based on A098550.
It appears (conjecture) that a(n)>1 for n>18. - Alexander R. Povolotsky, Dec 07 2014
Conjecture: a(n) = A247253(n-5) for n>12. - Reinhard Zumkeller, Dec 07 2014
The previous conjecture is equivalent to the statement that A251416(n) lists all primes and only primes after a(30)=18. - M. F. Hasler, Dec 08 2014
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
Let f(n)=A098551(A251595(n)). Then one can prove that A251417(n) = f(n) - f(n-1), n>=2. - Vladimir Shevelev, Dec 09 2014
EXAMPLE
See A251595.
MATHEMATICA
termsOfA251416 = 700;
f[lst_List] := Block[{k = 4}, While[GCD[lst[[-2]], k] == 1 || GCD[lst[[-1]], k] > 1 || MemberQ[lst, k], k++]; Append[lst, k]];
A098550 = Nest[f, {1, 2, 3}, termsOfA251416 - 3];
b[1] = 2;
b[n_] := b[n] = For[k = b[n-1], True, k++, If[FreeQ[A098550[[1 ;; n]], k], Return[k]]];
A251416 = Array[b, termsOfA251416];
PROG
(Haskell)
import Data.List (group)
a251417 n = a251417_list !! (n-1)
a251417_list = map length $ group a251416_list
-- Reinhard Zumkeller, Dec 05 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 03 2014
STATUS
approved