A098166 - OEIS

A098166

a(n) is the prime index of the Lesser Fortunate number A055211(n), or 0 if A055211(n) is not a prime.

2, 4, 5, 6, 7, 10, 9, 14, 13, 21, 17, 15, 24, 19, 21, 28, 24, 26, 31, 25, 23, 24, 25, 54, 32, 30, 36, 56, 54, 48, 41, 77, 60, 36, 45, 40, 52, 51, 43, 48, 48, 62, 108, 62, 88, 49, 64, 74, 55, 63, 65, 111, 69, 66, 63, 123, 91, 66, 83, 92, 97, 110, 67, 75, 99, 87

(list; graph; refs; listen; history; text; internal format)

OFFSET

2,1

LINKS

Jinyuan Wang, Table of n, a(n) for n = 2..2000

Antonín Čejchan, Michal Křížek, and Lawrence Somer, On Remarkable Properties of Primes Near Factorials and Primorials, Journal of Integer Sequences, Vol. 25 (2022), Article 22.1.4.

FORMULA

a(n) = A000720(A055211(n)) iff A055211(n) is a prime. - Michel Marcus, Oct 05 2019

PROG

(PARI) a(n) = {my(k = prod(j=1, n, prime(j))); p = k-precprime(k-2); if(isprime(p), primepi(p), 0); } \\ Jinyuan Wang, Oct 02 2019

CROSSREFS

Cf. A000720, A055211, A098167.

Sequence in context: A260820 A248554 A346993 * A217445 A007238 A083875

Adjacent sequences: A098163 A098164 A098165 * A098167 A098168 A098169

KEYWORD

nonn

AUTHOR

Pierre CAMI, Aug 30 2004

EXTENSIONS

Name edited by and more terms from Jinyuan Wang, Oct 02 2019

STATUS

approved