A215685 Smallest prime whose decimal expansion consists of the concatenation of a 2-digit emirp, a 3-digit emirp, a 4-digit emirp, ..., and an n-digit emirp (A006567).

13, 13337, 131071021, 13107100910711, 13107100910007100483, 131071009100071000491000187, 13107100910007100049100003310000657, 13107100910007100049100003310000169100007543, 131071009100071000491000033100001691000000071000015351

Offset: 2

Author

Jonathan Vos Post, Aug 20 2012

Keywords

• nonn
• base
• easy

Comments

If a(n) exists it has A000217(n)-1 digits.

Examples

			a(2) = 13 which is a prime, and whose decimal digits reversed, 31, is also a prime.
a(3) = 13337, which is a prime, and the concatenation of 13 (an emirp) and 337 (an emirp because 733 is also a prime). It happens that the digital reversal of a(3), 73331, is also prime, so that 13337 is an emirp, but that is not a requirement for this sequence.
Note that a(4) is a prime but not an emirp, because 12070131 = 3 * 61 * 65957.
		

Crossrefs

Cf. A000040, A006567, A215641, A215647.

Extensions

More terms from Alois P. Heinz, Aug 22 2012