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a(1) = 9; then numbers such that the concatenation a(n)a(n-1)...a(2)a(1)a(2)...a(n-1)a(n) is a prime for n>1.
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%I #12 Sep 01 2021 03:59:20

%S 9,1,7,17,9,9,1,51,29,21,49,107,37,63,329,69,93,1,53,9,79,219,267,59,

%T 457,189,599,277,743,67,59,379,33,231,83,381,451,11,451,791,289,323,

%U 87,241,447,189,189,1107,903,393,219,629,931,797,49,261,233,93,1239,663

%N a(1) = 9; then numbers such that the concatenation a(n)a(n-1)...a(2)a(1)a(2)...a(n-1)a(n) is a prime for n>1.

%e 191, 71917, 177191717, ... are prime.

%o (Python)

%o from sympy import isprime

%o def aupton(terms):

%o alst, astr = [9], "9"

%o for n in range(2, terms+1):

%o an = 1

%o while not isprime(int(str(an) + astr + str(an))): an += 1

%o alst.append(an); astr = str(an) + astr + str(an)

%o return alst

%o print(aupton(60)) # _Michael S. Branicky_, Sep 01 2021

%Y Cf. A083996, A083997, A083998, A083999, A084000, A084001, A084003.

%K base,nonn

%O 1,1

%A _Amarnath Murthy_, May 23 2003

%E More terms from _Ray Chandler_, Aug 03 2003