The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A254132 a(0)=1 and a(1)=2, then each term is x + y + x*y where x and y are the 2 last terms. 2

%I

%S 1,2,5,17,107,1943,209951,408146687,85691213438975,

%T 34974584955819144511487,2997014624388697307377363936018956287,

%U 104819342594514896999066634490728502944926883876041385836543

%N a(0)=1 and a(1)=2, then each term is x + y + x*y where x and y are the 2 last terms.

%H Ana Rechtman, <a href="http://images.math.cnrs.fr/Janvier-2015-3eme-defi.html">Janvier 2015, 3ème défi</a>, (in French), Images des Mathématiques, CNRS, 2015.

%H Ana Rechtman, <a href="http://images.math.cnrs.fr/Janvier-2015-4eme-defi.html">Solution</a>, (in French), Images des Mathématiques, CNRS, 2015.

%F a(n) = a(n-1) + a(n-2) + a(n-1)*a(n-2).

%F a(0) = 1 and a(n) = 2^Fibonacci(n)*3^Fibonacci(n+1) - 1 (see 2nd link).

%F a(n) == 8 mod 9, for n > 2. - _Ivan N. Ianakiev_, Jan 27 2015

%e a(0) = 1, a(1) = 2, a(2) = 1+2+(1*2) = 5, a(3) = 2+5+(2*5) = 17.

%t a254132[0]=1;a254132[n_]:=2^Fibonacci[n-1]*3^Fibonacci[n]-1;

%t a254132/@Range[0,11] (* _Ivan N. Ianakiev_, Jan 27 2015 *)

%o (PARI) lista(nn) = {x = 1; y = 2; print1(x, ", ", y, ", "); for (j=1, nn, z = x + y + x*y; print1(z, ", "); x = y; y = z;);}

%o (PARI) a(n) = if (!n, 1, 2^fibonacci(n)*3^fibonacci(n+1) - 1);

%Y Cf. A000045 (Fibonacci), A063896 (similar with initial values 0,1).

%Y Cf. A198796 (2^n*3^(n+1)-1).

%K nonn

%O 0,2

%A _Michel Marcus_, Jan 26 2015

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 16 21:26 EST 2020. Contains 331975 sequences. (Running on oeis4.)