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A151799 Version 2 of the "previous prime" function: largest prime < n. 72
2, 3, 3, 5, 5, 7, 7, 7, 7, 11, 11, 13, 13, 13, 13, 17, 17, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 29, 29, 31, 31, 31, 31, 31, 31, 37, 37, 37, 37, 41, 41, 43, 43, 43, 43, 47, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 53, 59, 59, 61, 61, 61, 61, 61, 61, 67, 67, 67, 67, 71, 71, 73, 73, 73, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Version 1 of the "previous prime" function is "largest prime <= n". This produces A007917, the same sequence of numerical values, except the offset (or indexing) starts at 2 instead of 3.

Maple's "prevprime" function uses version 2.

See A007917 for references and further information.

LINKS

Daniel Forgues, Table of n, a(n) for n = 3..100000

FORMULA

a(n) = A000040(A000720(n-1)). - Enrique Pérez Herrero, Jul 23 2011

a(n) = n + 1 - Sum_{k=1..n}( floor(k!^(n-1)/(n-1)!)-floor((k!^(n-1)-1)/(n-1)!) ). - Anthony Browne, May 17 2016

MAPLE

A151799:=n->prevprime(n): seq(A151799(n), n=3..100);

MATHEMATICA

Table[NextPrime[n, -1], {n, 3, 77}] (* Jean-François Alcover, May 27 2011 *)

PROG

(Maxima) makelist(prev_prime(n), n, 3, 79); /* Bruno Berselli, May 20 2011 */

(Haskell)

a151799 = a007917 . (subtract 1)  -- Reinhard Zumkeller, Jul 26 2012

(PARI) a(n)=precprime(n-1) \\ Charles R Greathouse IV, Jul 12 2016

(Python)

from sympy import prevprime

def A151799(n):

    return prevprime(n) # Chai Wah Wu, Feb 28 2018

CROSSREFS

Cf. A000040, A007917, A007918, A151800.

Sequence in context: A284412 A136548 A007917 * A305429 A093841 A281354

Adjacent sequences:  A151796 A151797 A151798 * A151800 A151801 A151802

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane, Jun 29 2009

STATUS

approved

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Last modified February 17 18:14 EST 2020. Contains 332005 sequences. (Running on oeis4.)