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A098166 a(n) is the prime index of the Lesser Fortunate number A055211(n), or 0 if A055211(n) is not a prime. 4

%I #21 May 22 2022 14:31:55

%S 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,

%T 30,36,56,54,48,41,77,60,36,45,40,52,51,43,48,48,62,108,62,88,49,64,

%U 74,55,63,65,111,69,66,63,123,91,66,83,92,97,110,67,75,99,87

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

%H Jinyuan Wang, <a href="/A098166/b098166.txt">Table of n, a(n) for n = 2..2000</a>

%H Antonín Čejchan, Michal Křížek, and Lawrence Somer, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL25/Krizek/krizek3.html">On Remarkable Properties of Primes Near Factorials and Primorials</a>, Journal of Integer Sequences, Vol. 25 (2022), Article 22.1.4.

%F a(n) = A000720(A055211(n)) iff A055211(n) is a prime. - _Michel Marcus_, Oct 05 2019

%o (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

%Y Cf. A000720, A055211, A098167.

%K nonn

%O 2,1

%A _Pierre CAMI_, Aug 30 2004

%E Name edited by and more terms from _Jinyuan Wang_, Oct 02 2019

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Last modified March 29 06:34 EDT 2024. Contains 371265 sequences. (Running on oeis4.)