cp's OEIS Frontend

A045798 Oddish numbers (prime to 10 and 10's digit is odd).

%I A045798 #32 Jul 09 2025 03:50:46
%S A045798 11,13,17,19,31,33,37,39,51,53,57,59,71,73,77,79,91,93,97,99,111,113,
%T A045798 117,119,131,133,137,139,151,153,157,159,171,173,177,179,191,193,197,
%U A045798 199,211,213,217,219,231,233,237,239,251,253,257,259
%N A045798 Oddish numbers (prime to 10 and 10's digit is odd).
%C A045798 From _Jianing Song_, Apr 27 2019: (Start)
%C A045798 Numbers congruent to {11, 13, 17, 19} mod 20.
%C A045798 Numbers k such that Kronecker(-20,k) = A289741(k) = -1. (End)
%H A045798 Reinhard Zumkeller, <a href="/A045798/b045798.txt">Table of n, a(n) for n = 1..10000</a>
%H A045798 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 1, -1).
%F A045798 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
%F A045798 a(n) = 5n + O(1). - _Charles R Greathouse IV_, Feb 07 2017
%F A045798 a(n+4) = a(n) + 20. This confirms Barker's conjecture. - _Robert Israel_, Mar 27 2017
%p A045798 seq(seq(20*j + k, k = [11, 13, 17, 19]),j=0..100); # _Robert Israel_, Mar 27 2017
%t A045798 Table[10n+{1,3,7,9},{n,1,31,2}]//Flatten (* _Harvey P. Dale_, Oct 01 2019 *)
%o A045798 (Haskell)
%o A045798 a045798 n = a045798_list !! (n-1)
%o A045798 a045798_list = filter (odd . (`mod` 10) . (`div` 10)) a045572_list
%o A045798 -- _Reinhard Zumkeller_, Dec 10 2011
%o A045798 (PARI) is(n)=gcd(n,10)==1 && n\10%2 \\ _Charles R Greathouse IV_, Feb 07 2017
%Y A045798 Complement of A045797 with respect to A045572.
%K A045798 nonn,base,easy,nice
%O A045798 1,1
%A A045798 _J. H. Conway_
%E A045798 More terms from _Erich Friedman_.