A127177 - OEIS

A127177

Primes whose "Look And Say" descriptions from right to left (in the sense of method A, i.e., frequency followed by digit-indication) are also primes.

%I #11 Jul 21 2017 16:36:52

%S 3,7,71,103,113,163,173,311,313,331,337,349,373,757,773,797,919,953,

%T 977,991,1109,1123,1151,1171,1181,1213,1237,1277,1279,1297,1327,1423,

%U 1447,1543,1553,1567,1621,1663,1669,1747,1811,1873,1877,1889,1993,1999,3049

%N Primes whose "Look And Say" descriptions from right to left (in the sense of method A, i.e., frequency followed by digit-indication) are also primes.

%e 71, 331 and 1277, for instance, belong to the sequence because their respective descriptions 1171 (one 1, one 7), 1123 (one 1, two 3's) and 271211 (two 7's, one 2, one 1) are primes.

%t LookAndSayA[ n_] := FromDigits@Flatten@((Through[ {Length, First}[ # ] ] &) /@ Split@Reverse@IntegerDigits@n); Select[Prime@Range[450],PrimeQ@LookAndSayA@# &] (* _Ray Chandler_, Jan 16 2007 *)

%Y Cf. A006711, A127178, A127179.

%K nonn,base

%O 1,1

%A _Lekraj Beedassy_, Jan 07 2007

%E Extended by _Ray Chandler_, Jan 16 2007