A256520 - OEIS

%I #12 Jun 25 2019 08:21:32

%S 83,84,95,46,443,255,182,557,1341,1107,526,553,923,114,1014,2255,1278,

%T 880,3039,796,1364,5212,2070,1252,1614,1544,496,4554,837,3013,3051,

%U 1788,1430,1628,7786,160,839,5825,5682,941,1066,10506,1977,655,1232,2288,4989

%N Number of primes between the n-th and (n+1)-st Carmichael numbers.

%H Amiram Eldar, <a href="/A256520/b256520.txt">Table of n, a(n) for n = 1..5000</a>

%t lst = Cases[Range[1, 100000, 2], n_ /; Mod[n, CarmichaelLambda@ n] == 1 && ! PrimeQ@ n]; Reap@ For[k = 1, k < Length@ lst, k++, Sow@ Count[Range[lst[[k]], lst[[k + 1]]], _?PrimeQ]] // Flatten // Rest (* _Michael De Vlieger_, Apr 03 2015, after _Artur Jasinski_ at A002997 *)

%o (PARI) vi=readvec("b002997.txt")

%o a(n)=primepi(vi[n+1])-primepi(vi[n])

%Y Cf. A002997.

%K nonn

%O 1,1

%A _Felix Fröhlich_, Apr 01 2015