%I #7 Apr 21 2018 17:35:32

%S 4,12,52,275,1539,8883,51974,306464,1815791,10791313,64266028,

%T 383289080,2288430270,13674181949,81759268145,489087871679,

%U 2926904894187,17521456528700,104917324472297,628377368081285,3764220848092978,22552713068921032,135139349515525416

%N The (6^n)-th composite number.

%F a[n] = PrimePi[a[n]]+6^n+1.

%e a[4] = 1539 = PrimePi[1539]+6^4+1 = 242+1296+1.

%t Composite[n_Integer] := Block[ {k = n + PrimePi[n] + 1 }, While[ k != n + PrimePi[k] + 1, k = n + PrimePi[k] + 1]; Return[ k ]]; Table[ Composite[6^n], {n, 0, 17} ]

%K nonn

%O 0,1

%A _Robert G. Wilson v_, Nov 27 2001

%E Corrected by _Vladeta Jovovic_, Dec 10 2001

%E a(18)-a(22) from _Chai Wah Wu_, Apr 21 2018