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A127178
Primes whose "Look And Say" descriptions from right to left (in the sense of method B, i.e., digit-indication followed by frequency) are also primes.
2
3, 7, 23, 59, 71, 83, 89, 103, 131, 233, 269, 311, 317, 349, 389, 409, 461, 479, 499, 547, 601, 619, 631, 641, 643, 683, 709, 719, 727, 733, 757, 787, 821, 853, 859, 911, 937, 971, 983, 1069, 1093, 1223, 1229, 1231, 1291, 1297, 1327, 1381, 1471, 1489, 1531
OFFSET
1,1
EXAMPLE
71, 499 and 1223, for instance, belong to the sequence because their respective descriptions 1171 (1 once, 7 once), 9241 (9 twice, 4 once), 312211 (3 once, 2 twice, 1 once) are all primes.
MATHEMATICA
LookAndSayB[ n_] := FromDigits@Flatten@((Through[ {First, Length}[ # ] ] &) /@ Split@Reverse@IntegerDigits@n); Select[Prime@Range[400], PrimeQ@LookAndSayB@# &] (* Ray Chandler, Jan 16 2007 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Lekraj Beedassy, Jan 07 2007
EXTENSIONS
Corrected by Ray Chandler, Jan 16 2007
STATUS
approved