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 A277351 #31 Jun 22 2025 15:11:23
%S A277351 5,14,19,44,53,62,71,152,169,186,203,220,237,254,271,560,593,626,659,
%T A277351 692,725,758,791,824,857,890,923,956,989,1022,1055,2144,2209,2274,
%U A277351 2339,2404,2469,2534,2599,2664,2729,2794,2859,2924,2989,3054,3119,3184,3249,3314
%N A277351 Value of (n+1,n) concatenated in binary representation.
%H A277351 Paolo P. Lava, <a href="/A277351/b277351.txt">Table of n, a(n) for n = 1..1000</a>
%F A277351 a(n) = (n+1) * 2^A070939(n) + n.
%F A277351 G.f.: (1-x)^(-2)*(5*x - 2*x^2 + Sum_{m>=1} ((2^(2*m)+2^m)*x^(2^m) - 2^(2*m)*x^(2^m+1))). - _Robert Israel_, Oct 14 2016
%e A277351 Binary representation of 12 and 13 are 1100 and 1101. Then, concat(1101,1100) = 11011100 converted in decimal representation is 220.
%p A277351 f:= n -> (n+1)*2^(1+ilog2(n))+n:
%p A277351 map(f, [$1..100]); # _Robert Israel_, Oct 14 2016
%t A277351 Table[FromDigits[Join @@ Map[IntegerDigits[#, 2] &, {n + 1, n}], 2], {n, 50}] (* _Michael De Vlieger_, Oct 14 2016 *)
%o A277351 (PARI) a(n) = subst(Pol(concat(binary(n+1), binary(n))), x, 2); \\ _Michel Marcus_, Oct 10 2016
%o A277351 (PARI) a(n) = (n+1)*2^(1+logint(n,2)) + n; \\ after Maple; _Michel Marcus_, Oct 15 2016
%o A277351 (Python)
%o A277351 def a(n): return int(bin(n+1)[2:] + bin(n)[2:], 2)
%o A277351 print([a(n) for n in range(1, 51)]) # _Michael S. Branicky_, May 14 2021
%Y A277351 Cf. A007088, A070939, A087737, A127423.
%K A277351 nonn,base,easy
%O A277351 1,1
%A A277351 _Paolo P. Lava_, Oct 10 2016