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 A100956 Consider all (2n+1)-digit palindromic primes of the form 70...0M0...07 (so that M is a palindrome with <= 2n-1 digits); a(n) = smallest such M. 3

%I

%S 2,2,141,2,545,5,141,282,111,3,141,5,131,282,141,141,9,3,2,303,171,6,

%T 222,323,2,393,797,606,191,404,414,363,797,171,474,737,25752,545,

%U 20502,14241,848,12821,15951,474,575,12321,2,17771,8,666,14541,15651,171,191

%N Consider all (2n+1)-digit palindromic primes of the form 70...0M0...07 (so that M is a palindrome with <= 2n-1 digits); a(n) = smallest such M.

%H Vincenzo Librandi, <a href="/A100956/b100956.txt">Table of n, a(n) for n = 1..200</a>

%t f[n_] := Block[{k = 0, t = Flatten[ Join[{7}, Table[0, {n - 1}]]]}, While[s = Drop[t, Min[ -Floor[ Log[10, k]/2], 0]]; k != FromDigits[ Reverse[ IntegerDigits[k]]] || !PrimeQ[ FromDigits[ Join[s, IntegerDigits[k], Reverse[s]]]], k++ ]; k]; Table[ f[n], {n, 55}]

%Y Cf. A100026, A100955, A100957.

%K base,nonn

%O 1,1

%A _Robert G. Wilson v_, Nov 23 2004

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Last modified February 26 17:19 EST 2020. Contains 332293 sequences. (Running on oeis4.)