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A330202
Palindromic primes p in base 10 such that 6*p+1 is also a palindromic prime in base 10.
1
131, 12130303121, 131302030203131, 12130313131303121, 13020303130302031, 13030212121203031, 1213130303030313121, 1312131302031312131, 121312031202130213121, 130212020303020212031, 130212121303121212031, 130312121202121213031, 12020312021312021302021, 12121212031213021212121
OFFSET
1,1
Each term starts with either 12 or 13. If a term is written as a0a1a2...a2a1a0, then a_i is either 0 or 1 when i is even and a_i is either 2 or 3 when i is odd (see A321210).
FORMULA
a(n) = (A321210(n)-1)/6.
PROG
(Python)
from sympy import isprime
A330202_list = []
for i in range(2**20):
s = bin(i)[2:]
s += s[-2::-1]
p = int(s) + int('02'*(len(s)//2)+'0')
q = 6*p+1
t = str(q)
if t == t[::-1] and isprime(p) and isprime(q):
A330202_list.append(p)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Chai Wah Wu, Dec 05 2019
STATUS
approved

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Last modified September 20 06:43 EDT 2024. Contains 376067 sequences. (Running on oeis4.)