This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A174091 #47 Aug 05 2023 13:10:34
%S A174091 2,3,2,3,6,7,6,7,10,11,10,11,14,15,14,15,18,19,18,19,22,23,22,23,26,
%T A174091 27,26,27,30,31,30,31,34,35,34,35,38,39,38,39,42,43,42,43,46,47,46,47,
%U A174091 50,51,50,51,54,55,54,55,58,59,58,59,62,63,62,63,66,67,66
%N A174091 a(n) = n OR 2.
%C A174091 OR(n, 2) + AND(n, 2) = n + 2.
%C A174091 OR(n, 2) - AND(n, 2) = n + 2*(-1)^floor(n/2), A004443.
%C A174091 a(n) = n when n = 2 or 3 mod 4 (n is in A042964). - _Alonso del Arte_, Feb 07 2013
%H A174091 Shane Chern, T. Cai, and H. Zhong, <a href="https://sites.psu.edu/shanechern/files/2017/12/On-reciprocal-sum-and-cardinality-of-primitive-sequences-2ioz54x.pdf">On the cardinality and sum of reciprocals of primitive sequences</a>, Preprint 2018; To appear in Adv. Math. (China).
%H A174091 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,-1).
%F A174091 a(n) = n + 1 + (-1)^floor(n/2).
%F A174091 G.f.: ( 2-x+x^3 ) / ( (1+x^2)*(x-1)^2 ). - _R. J. Mathar_, Feb 27 2013
%F A174091 Sum_{n>=0} (-1)^n/a(n) = Pi/4 - log(2)/2 = A196521. - _Peter McNair_, Aug 05 2023
%e A174091 a(3) = 3 because OR(0011, 0010) = 0011 = 3.
%e A174091 a(4) = 6 because OR(0100, 0010) = 0110 = 6.
%e A174091 a(5) = 7 because OR(0101, 0010) = 0111 = 7.
%p A174091 with(Bits): seq(Or(n,2), n=0..60);
%t A174091 Table[BitOr[n, 2], {n, 0, 100}] (* _Alonso del Arte_, Feb 06 2013 *)
%t A174091 LinearRecurrence[{2,-2,2,-1},{2,3,2,3},80] (* _Harvey P. Dale_, Oct 25 2016 *)
%o A174091 (PARI) a(n)=bitor(n,2) \\ _Charles R Greathouse IV_, Feb 27 2013
%Y A174091 Cf. similar sequences listed in A244587.
%Y A174091 Cf. A004443, A042964, A196521.
%K A174091 nonn,easy
%O A174091 0,1
%A A174091 _Gary Detlefs_, Feb 06 2013