A086402 Nontrivial numbers which are prime and yield another prime when their digits are sorted in descending order.

13, 17, 37, 79, 113, 131, 149, 157, 163, 167, 179, 181, 191, 197, 199, 241, 251, 281, 313, 337, 347, 359, 373, 389, 419, 461, 463, 491, 563, 571, 593, 613, 617, 683, 719, 787, 797, 839, 919, 1163, 1181, 1193, 1217, 1223, 1229, 1237, 1249, 1259, 1279, 1297

Offset: 1

Author

Chuck Seggelin, Jul 07 2003

Keywords

• base
• nonn

Comments

Primes with digits already in descending order (like 311 and 3221) are trivial cases and are therefore excluded.

Examples

			a(1)=13 because a descending sort of 13's digits yields 31 which is also prime. a(100)=2411 because a descending sort of 2411's digits yields 4211 which is also prime.
		

Crossrefs

Cf. A003459.

Programs

Mathematica

pdsdQ[p_]:=With[{d=FromDigits[ReverseSort[IntegerDigits[p]]]},d!=p&&PrimeQ[d]]; Select[Prime[Range[250]],pdsdQ] (* Harvey P. Dale, Oct 03 2024 *)