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A019464 Multiply by 1, add 1, multiply by 2, add 2, etc., start with 1. 10
1, 1, 2, 4, 6, 18, 21, 84, 88, 440, 445, 2670, 2676, 18732, 18739, 149912, 149920, 1349280, 1349289, 13492890, 13492900, 148421900, 148421911, 1781062932, 1781062944, 23153818272, 23153818285, 324153455990, 324153456004, 4862301840060, 4862301840075, 77796829441200 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..500

FORMULA

For n>=1, a(2n)=floor((1+e)*(n-1)!)-1, a(2n+1)=floor((1+e)*(n+1)!)-n-2. - Benoit Cloitre, Apr 29 2003

a(n+1) = (1/2) *a(n)*(n+1 mod 2)*(n+2)+1/2*(n mod 2)*(2*a(n)+n+1). - Francois Jooste (pin(AT)myway.com), Jun 25 2003

MATHEMATICA

a[n_?EvenQ] := n/2 + a[n-1]; a[n_?OddQ] := (n+1)*a[n-1]/2;

a[0] = 1; Table[a[n], {n, 0, 27}] (* Jean-Fran├žois Alcover, Nov 15 2011 *)

PROG

(Haskell)

a019464 n = a019464_list !! n

a019464_list = 1 : concat (unfoldr ma (1, [1, 1])) where

   ma (x, [_, j]) = Just (ij', (x + 1, ij')) where ij' = [x * j, x * j + x]

-- Reinhard Zumkeller, Nov 14 2011

(PARI) A019464(n, a=1)={for(i=2, n+1, if(bittest(i, 0), a+=i\2, a*=i\2)); a} \\ M. F. Hasler, Feb 25 2018

CROSSREFS

Cf. A033540 (=a(2n)).

Cf. A082458 (same, but start with 0), A019465 (start with 2), A019466 (start with 3).

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

Sequence in context: A067993 A074131 A309282 * A064402 A268577 A075229

Adjacent sequences:  A019461 A019462 A019463 * A019465 A019466 A019467

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Edited by M. F. Hasler, Feb 25 2018

STATUS

approved

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Last modified December 5 23:34 EST 2019. Contains 329782 sequences. (Running on oeis4.)