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Numbers n such that n*prime(n)-1 is a perfect square.
2

%I #9 May 21 2018 03:23:24

%S 1,10,50,4946,397706,1243141,3445873,9210805,805715770,1542576890

%N Numbers n such that n*prime(n)-1 is a perfect square.

%C Next term, if it exists, is > 400000. - 397706 from _Emeric Deutsch_, May 31 2005

%C a(11) > pi(4*10^12). - _Donovan Johnson_, Oct 22 2010

%C a(11) > pi(1.9*10^14). - _Giovanni Resta_, May 21 2018

%e 1*2-1=1^2

%e 10*29-1=17^2

%e 50*229-1=107^2

%e 4946*47981-1=15405^2

%K nonn

%O 1,2

%A _Zak Seidov_, May 06 2005

%E 397706 from _Emeric Deutsch_, May 31 2005

%E 4 more terms from _Ryan Propper_, Oct 16 2005

%E a(10) from _Donovan Johnson_, Oct 22 2010