%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