A391887 Alternately add and multiply the last two terms starting with 2, 1.

2, 1, 3, 3, 6, 18, 24, 432, 456, 196992, 197448, 38895676416, 38895873864, 1512881323731695591424, 1512881323770591465288, 2288809899755012359448064967916189926490112, 2288809899755012359449577849239960517955400

Offset

0,1

Comments

Uses the Lucas seed (2,1) instead of the Fibonacci seed (0,1) for generation.

Links

Table of n, a(n) for n=0..16.

Formula

a(n) = a(n-1) + a(n-2) if n is even, a(n) = a(n-1) * a(n-2) if n is odd; a(0)=2, a(1)=1.

Mathematica

a[n_] := a[n] = If[EvenQ[n], a[n-1] + a[n-2], a[n-1] * a[n-2]]; a[0] = 2; a[1] = 1; Array[a, 17, 0] (* Amiram Eldar, Dec 22 2025 *)

Crossrefs

Cf. A000032, A000204, A039941, A077753, A265496.

Sequence in context: A109522 A052959 A346473 * A257702 A338417 A034399

Adjacent sequences: A391884 A391885 A391886 * A391888 A391889 A391890

Keyword

nonn,easy

Author

Adolf Cusmariu, Dec 22 2025

Status

approved