A173101 Self-describing semiprimes.

22, 10183133, 10183331, 10213223, 10313317, 10322123, 10331831, 10331931, 10333117, 12183133, 12183331, 12193331, 12311033, 12311633, 12311833, 12313318, 12331031, 12333115, 12333119, 14103331, 14153331, 14163133, 14173133, 14183133, 14193331, 14311533, 14311633

Offset

1,1

Comments

This is to A001358 as A108810 is to A000040.

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Formula

{A109776 INTERSECTION A001358}. a(n) = n-th integer k such that OMEGA(k)=2 where OMEGA(n) is the sum of the exponents in the prime decomposition of k, and reading the number (in base 10) in successive pairs of digits gives a (possibly redundant) description of the number.

Example

a(1) = 22 because "22" does indeed consist of "two 2's" and 22 = 2 * 11 is semiprime. a(4) = 10213223 because 10213223 consists of one "0", two 1's, three 2's, and two 3's; and 10213223 = 41 * 249103 is semiprime.

Crossrefs

Cf. A001358, A108810, A109776.

Sequence in context: A267492 A013816 A104789 * A047841 A267498 A267497

Adjacent sequences: A173098 A173099 A173100 * A173102 A173103 A173104

Keyword

nonn,base,fini,less

Author

Jonathan Vos Post, Feb 09 2010

Extensions

More terms from Giovanni Resta, Aug 14 2019

Status

approved