OFFSET
1,1
COMMENTS
From Jianing Song, Apr 27 2019: (Start)
Numbers congruent to {11, 13, 17, 19} mod 20.
Numbers k such that Kronecker(-20,k) = A289741(k) = -1. (End)
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 1, -1).
FORMULA
Conjecture a(n) = a(n-1)+a(n-4)-a(n-5). G.f.: x*(11+2*x+4*x^2+2*x^3+x^4)/((1-x)^2*(1+x)*(1+x^2)). - Colin Barker, Apr 14 2012
a(n) = 5n + O(1). - Charles R Greathouse IV, Feb 07 2017
a(n+4) = a(n) + 20. This confirms Barker's conjecture. - Robert Israel, Mar 27 2017
MAPLE
seq(seq(20*j + k, k = [11, 13, 17, 19]), j=0..100); # Robert Israel, Mar 27 2017
MATHEMATICA
Table[10n+{1, 3, 7, 9}, {n, 1, 31, 2}]//Flatten (* Harvey P. Dale, Oct 01 2019 *)
PROG
(Haskell)
a045798 n = a045798_list !! (n-1)
a045798_list = filter (odd . (`mod` 10) . (`div` 10)) a045572_list
-- Reinhard Zumkeller, Dec 10 2011
(PARI) is(n)=gcd(n, 10)==1 && n\10%2 \\ Charles R Greathouse IV, Feb 07 2017
CROSSREFS
KEYWORD
nonn,base,easy,nice
AUTHOR
EXTENSIONS
More terms from Erich Friedman.
STATUS
approved