login
a(n) = least k such that n^n - k is prime.
8

%I #23 Jan 20 2019 15:42:40

%S 1,4,5,4,7,2,3,10,33,42,19,12,17,52,59,18,65,2,51,2,23,120,35,2,63,10,

%T 39,186,7,74,47,200,53,24,19,48,333,56,57,192,127,348,63,124,213,60,

%U 359,2,213,2,387,526,269,252,863,16,131,370,503,294,83,68,317

%N a(n) = least k such that n^n - k is prime.

%H Seiichi Manyama, <a href="/A074967/b074967.txt">Table of n, a(n) for n = 2..500</a>

%t PrimePrevDelta[n_]:=Module[{k},k=n-1;While[ !PrimeQ[k],k-- ];k=n-k]; lst={};Do[AppendTo[lst,PrimePrevDelta[n^n]],{n,2,5!}];lst (* _Vladimir Joseph Stephan Orlovsky_, Jun 11 2009 *)

%t lk[n_]:=Module[{nn=n^n},nn-NextPrime[nn,-1]]; Array[lk,70,2] (* _Harvey P. Dale_, Jan 20 2019 *)

%o (PARI) a(n)=(x->x-precprime(x))(n^n) \\ _Charles R Greathouse IV_, Nov 25 2014

%Y Cf. A033933, A074966.

%K nonn

%O 2,2

%A _Zak Seidov_, Oct 03 2002

%E More terms from _Robert G. Wilson v_, Oct 04 2002

%E Offset corrected by _R. J. Mathar_, Jun 12 2009