A108145 Smallest prime consisting of n successive positive integers in descending order followed by a 9. a(3*k) = 0 as no such prime exists.

19, 439, 0, 262524239, 765439, 0, 109876549, 1098765439, 0, 504948474645444342419, 27262524232221201918179, 0, 2019181716151413121110989, 64636261605958575655545352519, 0

Offset: 1

Author

Amarnath Murthy, Jan 01 2006

Keywords

• base
• nonn

Examples

			a(2) = 439, two successive positive integers 4,3 in descending order followed by a 9.
a(4) = 262524239 four successive positive integers 26,25,24,23 in descending order followed by a 9.
		

Crossrefs

Cf. A114754, A114755, A114756, A114757, A114758, A114759, A112716.

Programs

Mathematica

a[n_]:=If[Mod[n, 3]==0, 0, (For[m=1, (v={};Do[v=Join[v, IntegerDigits[k]], {k, m+n-1, m, -1}]);!PrimeQ[10FromDigits[v]+9], m++ ];10FromDigits[v]+9)];Table[a[n], {n, 16}] (* Farideh Firoozbakht *)
f[n_] := Block[{t = Reverse@Range@n}, If[ Mod[n, 3] == 0, 0, While[p = FromDigits@Flatten@IntegerDigits@Join[t, {9}]; !PrimeQ@p, t++ ]; p]]; Array[f, 16] (* Robert G. Wilson v *)

Extensions

Extended by Robert G. Wilson v, Ray Chandler and Farideh Firoozbakht, Jan 02 2006