A275680 Nonprime integers that become prime when concatenated with the next digit.

1, 9, 70, 10, 12, 72, 74, 30, 75, 14, 90, 76, 15, 16, 33, 18, 100, 91, 92, 93, 77, 34, 78, 700, 102, 104, 94, 105, 106, 35, 36, 702, 703, 95, 38, 39, 704, 300, 108, 705, 706, 96, 707, 98, 301, 99, 110, 302, 303, 710, 304, 111, 712, 112, 306, 115, 116, 308, 310, 900, 117, 118, 119, 312, 120, 121, 316, 318, 122, 319, 123, 124, 901, 125, 902, 904

Offset

1,2

Comments

The sequence is started with a(1) = 1 and always extended with the smallest integer not yet present that does not lead to a contradiction.

Links

Jean-Marc Falcoz, Table of n, a(n) for n = 1..10001

Example

1 is not prime but 19 is [1,9].
9 is not prime but 97 is [9,7(0)].
70 is not prime but 701 is [70,1(0)].
10 is not prime but 101 is [10,1(2)].
12 is not prime but 127 is [12,7(2)].
72 is not prime but 727 is [72,7(4)].
74 is not prime but 743 is [74,3(0)].
30 is not prime but 307 is [30,7(5)].
75 is not prime but 751 is [75,1(4)].
14 is not prime but 149 is [14,9(0)].
...

Crossrefs

Sequence in context: A152273 A217452 A193706 * A167534 A110202 A110201

Adjacent sequences: A275677 A275678 A275679 * A275681 A275682 A275683

Keyword

nonn,base

Author

Eric Angelini and Jean-Marc Falcoz, Aug 05 2016

Status

approved