A182364 a(1) = 0; a(n) = smallest integer not yet in this sequence S such that two neighboring digits of S sum to a semiprime (4, 6, 9, 10, 14, or 15).

0, 4, 2, 7, 3, 1, 5, 9, 6, 8, 13, 15, 18, 19, 51, 31, 33, 36, 37, 22, 24, 27, 28, 60, 40, 42, 45, 46, 81, 54, 55, 59, 63, 64, 68, 69, 131, 82, 72, 73, 77, 78, 133, 136, 86, 87, 222, 224, 227, 228, 137, 240, 90, 91, 95, 96, 313, 151, 315, 154, 242, 245, 155, 159, 181, 318, 182, 246, 319, 186, 331, 333, 187, 272, 273, 190, 404, 277, 278, 191, 336, 337, 281, 360, 406, 363, 195, 196, 364, 282, 286, 368, 287, 369, 513, 372, 409, 515, 422, 424, 518

Offset

1,2

Comments

This is to A001358 (semiprimes) as Eric Angelini's "Smallest integer not yet in S such that two neighboring digits of S sum up to a prime", is to A000040 (primes). Corrected and extended by Hans Havermann.

Links

Table of n, a(n) for n=1..101.

Example

a(2) = 4 because 4 is the smallest integer k such that a(0) + k is a semiprime (2*2 = 4).

Crossrefs

Cf. A001358.

Sequence in context: A272335 A198994 A368664 * A021238 A222622 A161179

Adjacent sequences: A182361 A182362 A182363 * A182365 A182366 A182367

Keyword

nonn,base,easy

Author

Jonathan Vos Post, Apr 27 2012

Status

approved