OFFSET
1,1
COMMENTS
It seems that most of the terms end with '9', followed by those ending with '3', '7', and '1'.
EXAMPLE
2 is a term because 2 is a prime with one '0' in binary form ('10') and '01' is not a prime. 2039 is a term because 2039 is a prime with one '0' in binary form ('11111110111') and changing the position of the '0', for example, '11111111011' = 2043 and '01111111111' = 1023, always results in a composite.
PROG
(Python)
from sympy import isprime
for n in range(1, 100):
s = n*'1'; c = 0
for j in range(n+1):
num = int(s[:j]+'0'+s[j:], 2)
if isprime(num):
c += 1
if c == 1: r = num
if c == 2: break
if c == 1: print(r, end = ', ')
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Ya-Ping Lu, Dec 23 2023
STATUS
approved