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A084002
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.
1
9, 1, 7, 17, 9, 9, 1, 51, 29, 21, 49, 107, 37, 63, 329, 69, 93, 1, 53, 9, 79, 219, 267, 59, 457, 189, 599, 277, 743, 67, 59, 379, 33, 231, 83, 381, 451, 11, 451, 791, 289, 323, 87, 241, 447, 189, 189, 1107, 903, 393, 219, 629, 931, 797, 49, 261, 233, 93, 1239, 663
OFFSET
1,1
EXAMPLE
191, 71917, 177191717, ... are prime.
PROG
(Python)
from sympy import isprime
def aupton(terms):
alst, astr = [9], "9"
for n in range(2, terms+1):
an = 1
while not isprime(int(str(an) + astr + str(an))): an += 1
alst.append(an); astr = str(an) + astr + str(an)
return alst
print(aupton(60)) # Michael S. Branicky, Sep 01 2021
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, May 23 2003
EXTENSIONS
More terms from Ray Chandler, Aug 03 2003
STATUS
approved