|
|
A340487
|
|
a(n) is the least prime that is the concatenation of two n-digit primes, or 0 if there are none.
|
|
2
|
|
|
23, 1117, 101107, 10091021, 1000710181, 100003100129, 10000031000171, 1000001910000349, 100000007100000541, 10000000071000000349, 1000000001910000000319, 100000000003100000000063, 10000000000391000000000903, 1000000000003710000000000259, 100000000000031100000000000403
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Conjecture: a(n) > 0 and the first n digits of a(n) = A003617(n). - Chai Wah Wu, Jan 13 2021
|
|
LINKS
|
|
|
EXAMPLE
|
a(3) = 101107 is prime and the concatenation of the two 3-digit primes 101 and 107.
|
|
MAPLE
|
f:= proc(d) local P, a, b;
a:= prevprime(10^(d-1));
do
a:= nextprime(a);
if a > 10^d then return FAIL fi;
b:= prevprime(10^(d-1));
do
b:= nextprime(b);
if b > 10^d then break fi;
if isprime(10^d*a+b) then return 10^d*a+b fi;
od od:
FAIL
end proc:
f(1):= 23:
map(f, [$1..20]);
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|