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A204541 Semiprimes with semiprime "look and say" descriptions. 1

%I

%S 4,14,15,21,22,35,38,55,57,74,87,95,119,143,145,166,187,205,215,217,

%T 247,253,254,259,278,287,289,291,305,314,335,339,341,394,403,407,427,

%U 471,493,505,514,515,517,538,553,559,565,589,614,622,623,629,633,634,649

%N Semiprimes with semiprime "look and say" descriptions.

%C Semiprime analogous to A056815.

%e 14 is in the sequence because 14 is a semiprime (2*7) and its "Look and Say", 1114 is also a semiprime (2*557).

%t LookAndSayA[n_] := FromDigits@ Flatten@ IntegerDigits@ Flatten[ Through[ {Length, First}[#]] & /@ Split@ IntegerDigits@ n]; semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; Select[ Range@ 650, semiPrimeQ@# && semiPrimeQ@ LookAndSayA@# &]

%Y Cf. A001358, A056815.

%K easy,nonn

%O 1,1

%A _Robert G. Wilson v_, Jan 27 2012

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Last modified January 24 06:41 EST 2022. Contains 350534 sequences. (Running on oeis4.)