login
A090559
Beginning with 2, least number such that concatenation of r copies of a(r), r = 1 to n is prime.
1
2, 1, 3, 1, 9, 3, 273, 219, 7, 281, 11, 119, 1019, 111, 47, 69, 171, 161, 103, 477, 817, 129, 271, 73, 1867, 381, 507, 113, 2643, 487, 3037, 727, 1109, 1789, 5829, 4937, 767, 12809, 1979, 587, 8417, 1623, 7233, 9079, 6739, 2269, 10251, 8911, 27881, 2691, 5257
OFFSET
1,1
COMMENTS
For n > 1, a(n) is odd and a(n) != 5 mod 10. - Chai Wah Wu, Jun 17 2019
EXAMPLE
2,211,211333,2113331111,211333111199999 are all prime.
CROSSREFS
Cf. A090560.
Sequence in context: A185176 A198315 A126761 * A088640 A186725 A301935
KEYWORD
base,more,nonn
AUTHOR
Amarnath Murthy, Dec 10 2003
EXTENSIONS
More terms from Max Alekseyev, Sep 04 2009
a(38)-a(51) from Chai Wah Wu, Jun 17 2019
STATUS
approved