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Multiply by 1, add 1, multiply by 2, add 2, etc.; start with 3.
10

%I #18 Oct 24 2024 15:28:44

%S 3,3,4,8,10,30,33,132,136,680,685,4110,4116,28812,28819,230552,230560,

%T 2075040,2075049,20750490,20750500,228255500,228255511,2739066132,

%U 2739066144,35607859872,35607859885,498510038390,498510038404,7477650576060,7477650576075,119642409217200

%N Multiply by 1, add 1, multiply by 2, add 2, etc.; start with 3.

%H Paolo Xausa, <a href="/A019466/b019466.txt">Table of n, a(n) for n = 0..800</a>

%t Module[{a = 3}, Join[{a}, Flatten[Array[{a *= #, a += #} &, 20]]]] (* _Paolo Xausa_, Oct 24 2024 *)

%o (PARI) A019466(n,a=3)={for(i=2,n+1,if(bittest(i,0),a+=i\2,a*=i\2));a} \\ _M. F. Hasler_, Feb 25 2018

%Y Cf. A082458 (same, but start with 0), A019464 (start with 1), A019465 (start with 2).

%Y Cf. A019460 .. A019463 & A082448 (similar, but first add, then multiply).

%K nonn

%O 0,1

%A _N. J. A. Sloane_

%E Edited by _M. F. Hasler_, Feb 25 2018