A151799 - OEIS

A151799

Version 2 of the "previous prime" function: largest prime < n.

123

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

a(n) = A060265(floor(n/2)) for n >= 4. - Georg Fischer, Nov 29 2022

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 *)