A274347 - OEIS

%I #13 Sep 03 2019 08:08:20

%S 12,21,28,33,44,54,72,77,87,116,126,141,188,198,203,228,304,319,329,

%T 369,492,517,522,532,597,796,836,846,861,966,1288,1353,1363,1368,1393,

%U 1563,2084,2189,2204,2214,2254,2529,3372,3542,3567,3572,3582,3647,4092

%N Products of two distinct Lucas numbers (3,4,7,11,18,...).

%C L(i)*L(j) = L(i+j) + (-1)^i*L(j-i). - _Robert Israel_, Sep 02 2019

%H Robert Israel, <a href="/A274347/b274347.txt">Table of n, a(n) for n = 1..10000</a>

%e 12 = 3*4, 21 = 3*7.

%p L:= gfun:-rectoproc({f(n+1)=f(n)+f(n-1),f(0)=2,f(1)=1},f(n),remember):

%p Q:= proc(n) local j; op(sort([seq(L(n)+(-1)^j*L(n-2*j),j=2..(n-1)/2)])) end proc:

%p map(Q, [$5..20]); # _Robert Israel_, Sep 02 2019

%t z = 100; f[n_] := LucasL[n];

%t Take[Sort[Flatten[Table[f[u] f[v], {u, 2, z}, {v, 2, u - 1}]]], z]

%Y Cf. A000032, A274348, A274349, A271354.

%K nonn,easy

%O 1,1

%A _Clark Kimberling_, Jun 18 2016