A112716 Smallest prime of the form: n successive positive integers in descending order followed by a 7.

17, 547, 3217, 65437, 543217, 8765437, 76543217, 41403938373635347, 9876543217, 282726252423222120197, 1312111098765437, 2322212019181716151413127, 222120191817161514131211107, 1615141312111098765437

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Example

a(4) = 65437, four successive positive integers 6,5,4,3 in descending order followed by a 7.

Mathematica

a[n_]:=(For[m=1, (v={}; Do[v=Join[v, IntegerDigits[k]], {k, m+n-1, m, -1}]); !PrimeQ[10FromDigits[v]+7], m++ ]; 10FromDigits[v]+7); Table[a[n], {n, 14}] - Farideh Firoozbakht
f[n_] := Block[{t = Reverse@Range@n}, While[p = FromDigits@Flatten@IntegerDigits@Join[t, {7}]; !PrimeQ@p, t++ ]; p]; Array[f, 14] (* Robert G. Wilson v *)

Crossrefs

Cf. A114754, A114755, A114756, A114757, A114758, A114759, A108145.

Sequence in context: A214135 A193120 A264858 * A218351 A197395 A280181

Adjacent sequences: A112713 A112714 A112715 * A112717 A112718 A112719

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