# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a102589 Showing 1-1 of 1 %I A102589 #6 Oct 04 2013 15:53:33 %S A102589 124,421,1324,4231,13324,42331,1333324,4233331 %N A102589 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 A102589 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 A102589 124 and 421 are in the sequence because 124=4*31 and both numbers %e A102589 31=(10^2-7)/3 and 421=(127*10^(2-1)-7)/3 are primes. It seems that %e A102589 there is no further term. %Y A102589 Cf. A069514, A102285. %K A102589 nonn %O A102589 1,1 %A A102589 _Farideh Firoozbakht_, Jan 22 2005 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE