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 A234095 #27 Sep 08 2022 08:46:06 %S A234095 7,17,19,43,47,59,61,71,79,101,107,109,149,151,163,167,197,223,257, %T A234095 263,271,311,317,347,349,353,383,389,401,421,439,449,461,479,503,521, %U A234095 523,557,569,599,601,613,631,673,677,691,701,811,821,827,839,853,863,881 %N A234095 Primes p such that 2*p + 1 is semiprime. %C A234095 Also primes of the form (p*q - 1)/2, where p and q are distinct primes. %H A234095 Harvey P. Dale, <a href="/A234095/b234095.txt">Table of n, a(n) for n = 1..1000</a> %F A234095 2*a(n)+1 = A233561(n). - _R. J. Mathar_, Aug 30 2016 %e A234095 7 is in the sequence because it is prime and 7*2 + 1 = 15 = 3*5 is a semiprime. %t A234095 t = Select[Range[1, 7000, 2], Map[Last, FactorInteger[#]] == Table[1, {2}] &]; Take[(t - 1)/2, 120] (* A234093 *) %t A234095 v = Flatten[Position[PrimeQ[(t - 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}] (* A233561 *) %t A234095 (w - 1)/2 (* A234095 *) (* _Peter J. C. Moses_, Dec 23 2013 *) %t A234095 Select[Prime[Range[200]],PrimeOmega[2#+1]==2&] (* _Harvey P. Dale_, Mar 19 2015 *) %o A234095 (PARI) is(n)=isprime(n) && bigomega(2*n+1)==2 \\ _Charles R Greathouse IV_, Feb 19 2014 %o A234095 (Magma) IsSemiprime:=func< p | &+[ k[2]: k in Factorization(p)] eq 2 >; [p: p in PrimesUpTo(1000)| IsSemiprime(2*p+1)]; // _Vincenzo Librandi_, Feb 21 2014 %Y A234095 Cf. A233561, A234096, A233562. %K A234095 nonn,easy %O A234095 1,1 %A A234095 _Clark Kimberling_, Dec 27 2013 %E A234095 New name from _Zak Seidov_, Feb 19 2014