OFFSET
1,2
COMMENTS
From Jianing Song, Apr 27 2019: (Start)
Numbers congruent to {1, 3, 7, 9} mod 20.
Numbers k such that Kronecker(-20,k) = A289741(k) = +1. (End)
First 20 terms are congruences of 3^k mod 100. - Dario Vuksan, Jan 09 2023
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*(1+2*x+4*x^2+2*x^3+11*x^4) / ((1-x)^2*(1+x)*(1+x^2)). - Colin Barker, Apr 14 2012
The conjecture above is correct. - Jianing Song, Apr 27 2019
a(n) = 5n + O(1). - Charles R Greathouse IV, Jan 09 2023
MATHEMATICA
Flatten[Table[10n+{1, 3, 7, 9}, {n, 0, 30, 2}]] (* Harvey P. Dale, Dec 05 2012 *)
PROG
(Haskell)
a045797 n = a045797_list !! (n-1)
a045797_list = filter (even . (`mod` 10) . (`div` 10)) a045572_list
-- Reinhard Zumkeller, Dec 10 2011
(PARI) is(n)=gcd(n, 10)==1 && n\10%2==0 \\ Charles R Greathouse IV, Sep 24 2015
CROSSREFS
KEYWORD
nonn,base,easy,nice
AUTHOR
EXTENSIONS
More terms from Erich Friedman
Offset changed by Reinhard Zumkeller, Dec 10 2011
STATUS
approved