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%I #6 Oct 04 2013 15:53:33
%S 124,421,1324,4231,13324,42331,1333324,4233331
%N Numbers of the forms 4*p or q where both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes.
%C This sequence is a subsequence of A069514 (If m is in the sequence then sigma(reversal(m)) = reversal(sigma(m))), so see Comments on A069514. There exists only four known n's such that both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes, n=2,3, 4 and 6.
%e 124 and 421 are in the sequence because 124=4*31 and both numbers
%e 31=(10^2-7)/3 and 421=(127*10^(2-1)-7)/3 are primes. It seems that
%e there is no further term.
%Y Cf. A069514, A102285.
%K nonn
%O 1,1
%A _Farideh Firoozbakht_, Jan 22 2005
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