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A108145 Smallest prime consisting of n successive positive integers in descending order followed by a 9. a(3k) = 0 as no such prime exists. 7
19, 439, 0, 262524239, 765439, 0, 109876549, 1098765439, 0, 504948474645444342419, 27262524232221201918179, 0, 2019181716151413121110989, 64636261605958575655545352519, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..15.

EXAMPLE

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.

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 *)

CROSSREFS

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

Sequence in context: A284332 A121938 A291644 * A114350 A194730 A012506

Adjacent sequences:  A108142 A108143 A108144 * A108146 A108147 A108148

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Jan 01 2006

EXTENSIONS

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

STATUS

approved

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Last modified August 2 01:19 EDT 2021. Contains 346408 sequences. (Running on oeis4.)