A215685 - OEIS

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

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OFFSET

2,1

COMMENTS

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

LINKS

Table of n, a(n) for n=2..10.

EXAMPLE

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.

Sequence in context: A189309 A203707 A176096 * A327585 A262810 A340295

Adjacent sequences: A215682 A215683 A215684 * A215686 A215687 A215688

KEYWORD

nonn,base,easy

AUTHOR

Jonathan Vos Post, Aug 20 2012

EXTENSIONS

More terms from Alois P. Heinz, Aug 22 2012

STATUS

approved