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%I #13 Dec 12 2013 18:52:28
%S 15,95,287,1199,4607,23519,28799,101567,223199,296207,352799,903167,
%T 1019999,2032127,2230799,2666159,3285599,5896799,7606367,13939199,
%U 19392479,28839887,36154799,46139039,54295919,62412767,68250239,73384079,74440799,90316799,95234687,109672319,115263647,118129199,214562399,223279487,234503807,236792879,262963199,270420767,309829727,355897439,422999999,486823247,589884959,628687487
%N Numbers n such that n'= p^2 -1, with n = semiprime = p*q, n' is the arithmetic derivative of n. Also: semiprimes of the form p*(p^2-p-1)
%C The sequence shows similarity with the Rassias Conjecture "for any prime p there are two primes p1 and p2 such that p*p1=p1+p2+1, p>2, p2>p1") with p1=p we have p*p=p+p2-1 (see A190272). Generalization can be achieved by removing semiprimarity condition and accepting p^e, e>=2.
%H European Mathematical Society, <a href="http://www.ems-ph.org/journals/newsletter/pdf/2011-03-79.pdf">Newsletter (see book reviews)</a>, March 2011, page 46
%e n=15, 15'=8, a=8+1=9=3^2 -> a(1)=15
%p seq(`if`(isprime((ithprime(i)^2-ithprime(i)-1))=true,(ithprime(i)^2-ithprime(i)-1)*ithprime(i),NULL),i=1..300);
%Y Cf. A001358 (semiprime), A003415 (arithmetic derivative), A190273 (n'=a-1), A190273 (n'=a+1)
%K nonn
%O 1,1
%A _Giorgio Balzarotti_, May 07 2011
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