login
A045798
Oddish numbers (prime to 10 and 10's digit is odd).
15
11, 13, 17, 19, 31, 33, 37, 39, 51, 53, 57, 59, 71, 73, 77, 79, 91, 93, 97, 99, 111, 113, 117, 119, 131, 133, 137, 139, 151, 153, 157, 159, 171, 173, 177, 179, 191, 193, 197, 199, 211, 213, 217, 219, 231, 233, 237, 239, 251, 253, 257, 259
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)
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
Complement of A045797 with respect to A045572.
Sequence in context: A168446 A275467 A376303 * A267277 A155071 A003626
KEYWORD
nonn,base,easy,nice
AUTHOR
EXTENSIONS
More terms from Erich Friedman.
STATUS
approved