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A090270
Least positive r such that concatenation k, r, k is prime, where k == 1,3,7 or 9 (mod 10) in increasing order.
2
3, 1, 2, 1, 3, 3, 1, 2, 1, 6, 1, 1, 2, 5, 3, 1, 1, 5, 1, 5, 1, 3, 4, 1, 2, 4, 5, 22, 1, 6, 3, 2, 1, 3, 1, 1, 2, 4, 3, 14, 12, 15, 4, 3, 4, 1, 1, 1, 2, 14, 3, 4, 1, 3, 1, 8, 1, 4, 5, 6, 3, 4, 14, 1, 1, 5, 3, 3, 2, 6, 1, 3, 26, 2, 6, 1, 7, 2, 3, 21, 1, 3, 2, 6, 3, 2, 9, 10, 4, 3, 15, 9, 4, 7, 5, 1, 3, 5, 5, 5, 16
OFFSET
1,1
EXAMPLE
131,313,727,919,11311,... etc. are primes.
CROSSREFS
Cf. A090271.
Sequence in context: A370897 A146969 A338804 * A326441 A178830 A029329
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Nov 28 2003
EXTENSIONS
More terms from Joshua Zucker, May 03 2006
STATUS
approved