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A108278 Numbers n such that n^2-1 and n^2+1 are semiprimes. 1


%S 12,30,42,60,102,108,198,312,462,522,600,810,828,1020,1050,1062,1278,

%T 1452,1488,1872,1950,2028,2130,2142,2340,2790,2802,2970,3000,3120,

%U 3252,3300,3330,3672,3930,4020,4092,4230,4548,4800,5280,5640,5652,5658,6198

%N Numbers n such that n^2-1 and n^2+1 are semiprimes.

%e a(1)=12 because 12^2-1=143=11*13 and 12^2+1=145=5*29 are both semiprimes.

%Y Cf. A001358 semiprimes, A069062 n^2-1 and n^2+1 have the same number of divisors.

%K nonn

%O 1,1

%A _Hugo Pfoertner_, May 30 2005

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Last modified April 19 08:09 EDT 2014. Contains 240739 sequences.