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A336298 Greatest prime < prime(n)/2. 2
2, 3, 5, 5, 7, 7, 11, 13, 13, 17, 19, 19, 23, 23, 29, 29, 31, 31, 31, 37, 41, 43, 47, 47, 47, 53, 53, 53, 61, 61, 67, 67, 73, 73, 73, 79, 83, 83, 89, 89, 89, 89, 97, 97, 103, 109, 113, 113, 113, 113, 113, 113, 127, 131, 131, 131, 137, 139, 139, 139, 151, 151 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

The n-th prime appears A102820(n) times. - Flávio V. Fernandes, Apr 08 2021

LINKS

Table of n, a(n) for n=3..64.

FORMULA

a(n) = A151799(A000040(n)/2) for n >= 3. - Wesley Ivan Hurt, Nov 26 2020

EXAMPLE

Prime(3)/2 = 2.5, so that a(3) = 2.

MATHEMATICA

z = 120; t = Table[NextPrime[Prime[n]/2], {n, 3, z}]; (* A039734, A079953 *)

u = NextPrime[t, -1]  (* A336298 *)

t - u (* A336299 *)

Table[NextPrime[Prime[n]/2, -1], {n, 3, 80}] (* Wesley Ivan Hurt, Nov 26 2020 *)

PROG

(PARI) a(n) = precprime(prime(n)/2); \\ Michel Marcus, Nov 16 2020

(Python)

from sympy import prime, prevprime

def A336298(n):

    return prevprime(prime(n)//2+1) # Chai Wah Wu, Nov 26 2020

CROSSREFS

Cf. A000040, A039734, A336299.

Sequence in context: A234345 A111060 A082432 * A037153 A323185 A168065

Adjacent sequences:  A336295 A336296 A336297 * A336299 A336300 A336301

KEYWORD

nonn,changed

AUTHOR

Clark Kimberling, Nov 16 2020

STATUS

approved

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Last modified April 21 03:28 EDT 2021. Contains 343145 sequences. (Running on oeis4.)