OFFSET
1,1
COMMENTS
Numbers of the form prime(k)^a(n) do not appear in A026477.
Terms are all the positive integers except 1, 2, 4 and numbers of the form 7k+1.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,1,-1).
FORMULA
For n>=2, a(n) = n + ceiling((n+2)/6) + 2.
For n>=8, a(n) = a(n-6) + 7.
G.f.: (3+2*x+x^2+x^3+2*x^4+x^5-2*x^6-x^7)/(1-x-x^6+x^7). - Robert Israel, Sep 09 2016
MAPLE
3, seq(n + ceil((n+2)/6)+2, n=2..100); # Robert Israel, Sep 09 2016
MATHEMATICA
Join[{3}, LinearRecurrence[{1, 0, 0, 0, 0, 1, -1}, {5, 6, 7, 9, 10, 11, 12}, 100]] (* Vincenzo Librandi, Aug 27 2016 *)
PROG
(PARI) a(n)=if(n>1, n+(n+7)\6, 2) \\ Charles R Greathouse IV, Aug 27 2016
(PARI) Vec((3+2*x+x^2+x^3+2*x^4+x^5-2*x^6-x^7)/(1-x-x^6+x^7) + O(x^99)) \\ Altug Alkan, Sep 09 2016
(Magma) [n+Ceiling((n+2)/6)+2: n in [0..100]]; // Vincenzo Librandi, Aug 27 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Bob Selcoe, Aug 26 2016
STATUS
approved