A336298 - OEIS

%I #48 Jun 05 2023 01:13:30

%S 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,

%T 53,53,53,61,61,67,67,73,73,73,79,83,83,89,89,89,89,97,97,103,109,113,

%U 113,113,113,113,113,127,131,131,131,137,139,139,139,151,151

%N Greatest prime < prime(n)/2.

%C The n-th prime appears A102820(n) times. - _Flávio V. Fernandes_, Apr 08 2021

%C A080191 lists the distinct terms of this sequence. - _Flávio V. Fernandes_, Jun 19 2021

%F a(n) = A151799(A000040(n)/2) for n >= 3. - _Wesley Ivan Hurt_, Nov 26 2020

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

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

%t u = NextPrime[t, -1]  (* A336298 *)

%t t - u (* A336299 *)

%t Table[NextPrime[Prime[n]/2, -1], {n, 3, 80}] (* _Wesley Ivan Hurt_, Nov 26 2020 *)

%o (PARI) a(n) = precprime(prime(n)/2); \\ _Michel Marcus_, Nov 16 2020

%o (Python)

%o from sympy import prime, prevprime

%o def A336298(n):

%o     return prevprime(prime(n)//2+1) # _Chai Wah Wu_, Nov 26 2020

%Y Cf. A000040, A039734, A336299.

%K nonn

%O 3,1

%A _Clark Kimberling_, Nov 16 2020