A249406 - OEIS

%I #18 May 09 2021 02:51:53

%S 1,6,20,56,90,132,182,240,306,399,506,600,702,812,930,1056,1190,1332,

%T 1482,1640,1806,1980,2162,2352,2550,2756,2970,3306,3540,3782,4032,

%U 4290,4556,4830,5112,5402,5700,6006,6320,6642,6972,7310,7656,8099,8556,8930,9312

%N Start with a(1) = 1, and extend by the rule that the next term is the product of the two most recent non-terms of the sequence.

%C Compare to A075326, where not products, but sums of the two most recent non-terms are considered;

%C a(195) = 159200 is the smallest even term not of the form m*(m+1); see also A249408, the set of all non-oblong terms of this sequence.

%C a(10) = 399 is the smallest odd term.

%H Reinhard Zumkeller, <a href="/A249406/b249406.txt">Table of n, a(n) for n = 1..10000</a>

%o (Haskell)

%o import Data.List ((\\))

%o a249406 n = a249406_list !! (n-1)

%o a249406_list = 1 : f [2..] where

%o    f ws@(u:v:_) = y : f (ws \\ [u, v, y]) where y = u * v

%Y Cf. A000301, A000304, A075326, A249055, A249407 (complement), subsequence of A002808.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Oct 31 2014