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Products of two primes whose difference is a perfect square.
2

%I #7 Mar 11 2019 03:04:46

%S 6,21,22,57,77,161,166,201,205,221,301,309,377,437,454,497,517,597,

%T 745,749,886,901,1057,1357,1457,1461,1469,1517,1577,1841,1961,2021,

%U 2041,2077,2182,2317,2361,2537,2701,3046,3097,3397,3437,3497,3737,3841,3901

%N Products of two primes whose difference is a perfect square.

%e 57 = 19*3 and 19 - 3 = 16 = 4^2.

%p with(numtheory): a:=proc(n) if bigomega(n)=2 and nops(factorset(n))=2 and type(sqrt(factorset(n)[2]-factorset(n)[1]),integer)=true then n else end if end proc: seq(a(n),n=1..4000); # _Emeric Deutsch_, Aug 16 2008

%t Take[ Sort[ Times @@@ Select[ Subsets[ Array[ Prime, 310], {2}], IntegerQ[ Sqrt[ #[[2]] - #[[1]] ]] &]], 48] (* _Robert G. Wilson v_ *)

%Y Cf. A141755.

%K nonn

%O 1,1

%A David Spector (spectord(AT)ccsu.edu), Aug 13 2008

%E Extended by _Emeric Deutsch_, Aug 16 2008