The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A033556 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A033556

a(n+1) = 2a(n) - {largest prime < a(n)}.
(history; published version)

#24 by N. J. A. Sloane at Sun Oct 22 01:34:55 EDT 2017

STATUS

reviewed

approved

#23 by G. C. Greubel at Sat Oct 21 23:06:31 EDT 2017

STATUS

proposed

reviewed

#22 by Iain Fox at Sat Oct 21 17:49:19 EDT 2017

STATUS

editing

proposed

Discussion

Sat Oct 21

18:15

David A. Corneth: Leave it as is, it's fine.

#21 by Iain Fox at Sat Oct 21 17:47:21 EDT 2017

PROG

(PARI) a(n) = if(n==0, return(3), return(, 2*a(n-1)-precprime(a(n-1)-1))) \\ Iain Fox, Oct 18 2017

STATUS

proposed

editing

Discussion

Sat Oct 21

17:48

Iain Fox: Since my PARI code is much slower, should I get rid of it or make a note next to it noting its lack of efficiency.

#20 by David A. Corneth at Wed Oct 18 17:05:05 EDT 2017

STATUS

editing

proposed

#19 by David A. Corneth at Wed Oct 18 17:03:05 EDT 2017

PROG

(PARI) first(n) = my(res = vector(n)); res[1] = 3; for(i = 2, n, res[i] = 2 * res[i - 1] - precprime(res[i - 1] - 1)); res \\ David A. Corneth, Oct 18 2017

Discussion

Wed Oct 18

17:03

David A. Corneth: Let's save ourselves a lot of calls of a(n).

#18 by David A. Corneth at Wed Oct 18 16:59:29 EDT 2017

CROSSREFS

Cf. A007917, A151799.

STATUS

proposed

editing

#17 by Michel Marcus at Wed Oct 18 16:55:18 EDT 2017

STATUS

editing

proposed

#16 by Michel Marcus at Wed Oct 18 16:54:08 EDT 2017

PROG

(PARI) a(n) = if(n==0, return(3), return(2*a(n-1)-precprime(a(n-1)-1))) \\_ _Iain Fox_, Oct 18 2017

STATUS

reviewed

editing

Discussion

Wed Oct 18

16:55

Michel Marcus: could also be a(n) = if(n==0, 3, 2*a(n-1)-precprime(a(n-1)-1)) without the returns

#15 by Andrey Zabolotskiy at Wed Oct 18 16:11:35 EDT 2017

STATUS

proposed

reviewed