A057034 - OEIS

%I #9 May 20 2022 08:31:49

%S 3,2,5,2,5,4,7,4,7,4,23,2,19,2,97,2,19,64,17,62,19,4,17,58,23,64,157,

%T 122,47,106,47,4,29,146,31,64,29,8,71,8,43,32,31,128,67,122,41,2,37,

%U 146,137,122,191,142,59,128,71,284,109,274,101,218,97,32,83,158,53,166

%N Difference between n!! and the first prime before n!! - 1.

%C Analogous to the lesser Fortunate numbers but unlike them, all entries are not prime. Must odd entries are powers of two and all even entries are primes.

%t PrevPrime[ n_Integer ] := (k=n-1; While[ !PrimeQ[ k ], k-- ]; Return[ k ]); f[ n_Integer ] := (p = n!! - 1; q = PrevPrime[ p ]; Return[ p - q + 1 ]); Table[ f[ n ], {n, 4, 75} ]

%Y Cf. A006882, A057019.

%K nonn

%O 4,1

%A _Robert G. Wilson v_, Sep 09 2000