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

Author

Jonathan Vos Post, Feb 09 2010

Keywords

• nonn
• base
• fini
• less

Comments

This is to A001358 as A108810 is to A000040.

Examples

			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.
		

Links

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

Crossrefs

Cf. A001358, A108810, A109776.

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.

Extensions

More terms from Giovanni Resta, Aug 14 2019