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A069566
a(1)=0; for n >= 2, a(n) = smallest value of k such that the concatenation 1,n,n^2,..., n^(k-1), n^k,n^(k-1),...n^2,n,1 is a prime.
1
0, 2, 1, 12, 1, 2
OFFSET
1,2
COMMENTS
Terms from Robert G. Wilson v.
EXAMPLE
a(2) = 2 as 12421 is a prime.
MATHEMATICA
Do[k = 0; While[a = Table[n^i, {i, 0, k}]; b = ToExpression[ StringJoin[ ToString /@ Join[a, Drop[ Reverse[a], 1]]]]; !PrimeQ[b], k++ ]; Print[b], {n, 2, 10} ] (* Robert G. Wilson v *)
CROSSREFS
See A239908 for another version.
Sequence in context: A285649 A074956 A176088 * A336314 A066818 A005730
KEYWORD
more,nonn,base
AUTHOR
Amarnath Murthy, Mar 24 2002
STATUS
approved