OFFSET
1,1
COMMENTS
"Replacing each digit d with d copies of the digit d" is the function A048376, well defined on the set of positive integers. Therefore (the range of) the present sequence is the largest subset of A000040 stable under the operation A048376.
A004022 is a subsequence. - Chai Wah Wu, Dec 19 2019
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000
EXAMPLE
E.g. 641 becomes 66666644441 which is also prime.
MATHEMATICA
Select[Prime[Range[500]], PrimeQ[FromDigits[Flatten[Table[#, {#}]&/@ IntegerDigits[ #]]]]&] (* Harvey P. Dale, Dec 18 2010 *)
PROG
(Python)
from sympy import isprime, nextprime
A057630_list, dlist, p = [], [str(d)*d for d in range(10)], 2
while len(A057630_list) < 10000:
if isprime(int(''.join(dlist[int(d)] for d in str(p)))):
A057630_list.append(p)
p = nextprime(p) # Chai Wah Wu, Dec 19 2019, corrected Jan 01 2022
CROSSREFS
KEYWORD
nonn,base,nice,easy
AUTHOR
G. L. Honaker, Jr., Oct 10 2000
EXTENSIONS
More terms from Patrick De Geest, Oct 15 2000
Offset changed to 1, according to OEIS conventions, by M. F. Hasler, Jan 23 2013
STATUS
approved