This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A190274 #16 Oct 20 2024 02:08:37
%S A190274 15,95,287,1199,4607,23519,28799,101567,223199,296207,352799,903167,
%T A190274 1019999,2032127,2230799,2666159,3285599,5896799,7606367,13939199,
%U A190274 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 A190274 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 A190274 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 A190274 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 A190274 n=15, 15'=8, a=8+1=9=3^2 -> a(1)=15
%p A190274 seq(`if`(isprime((ithprime(i)^2-ithprime(i)-1))=true,(ithprime(i)^2-ithprime(i)-1)*ithprime(i),NULL),i=1..300);
%Y A190274 Cf. A001358 (semiprime), A003415 (arithmetic derivative), A190273 (n'=a-1), A190273 (n'=a+1).
%K A190274 nonn
%O A190274 1,1
%A A190274 _Giorgio Balzarotti_, May 07 2011