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A112716
Smallest prime of the form: n successive positive integers in descending order followed by a 7.
7
17, 547, 3217, 65437, 543217, 8765437, 76543217, 41403938373635347, 9876543217, 282726252423222120197, 1312111098765437, 2322212019181716151413127, 222120191817161514131211107, 1615141312111098765437
OFFSET
1,1
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 *)
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Jan 01 2006
EXTENSIONS
STATUS
approved