Search: id:A005383
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%I A005383 M2492
%S A005383 3,5,13,37,61,73,157,193,277,313,397,421,457,541,613,661,673,733,757,
%T A005383 877,997,1093,1153,1201,1213,1237,1321,1381,1453,1621,1657,1753,1873,
%U A005383 1933,1993,2017,2137,2341,2473,2557,2593,2797,2857,2917,3061,3217,3253
%N A005383 Numbers n such that both n and (n+1)/2 are primes.
%C A005383 Also, n such that sigma(n)/2 is prime. - Joseph L. Pe (joseph_l_pe(AT)hotmail.com), 
               Dec 10 2001; confirmed by Vladeta Jovovic, Dec 12, 2002.
%C A005383 Or, primes p such that p+1 is a semiprime. - Zak Seidov (zakseidov(AT)yahoo.com), 
               Jul 01 2005
%D A005383 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A005383 M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, 
               National Bureau of Standards Applied Math. Series 55, 1964 (and various 
               reprintings), p. 870.
%H A005383 T. D. Noe, <a href="b005383.txt">Table of n, a(n) for n=1..10000</a>
%H A005383 M. Abramowitz and I. A. Stegun, eds., <a href="http://www.nrbook.com/
               abramowitz_and_stegun/">Handbook of Mathematical Functions</a>, National 
               Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 
               [alternative scanned copy].
%F A005383 a(n) = A129521(n)/A005382(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Apr 19 2007
%t A005383 A005383=Select[Prime[Range[1000]], Plus@@Last/@FactorInteger[ #+1]==2&] 
               (Seidov)
%o A005383 (Matlab) LIMIT = 8000 % Find all members of A005383 less than LIMIT A 
               = primes(LIMIT); n = length(A); %n is number of primes less than 
               LIMIT B = 2*A - 1; C = ones(n, 1)*A; %C is an n X n matrix, with 
               C(i, j) = j-th prime D = B'*ones(1, n); %D is an n X n matrix, with 
               D(i, j) = (ith prime)*2 - 1 [i, j] = find(C == D); A(j)
%Y A005383 Cf. A005382, A057326, A057327, A057328, A057329, A057330, A005603.
%Y A005383 Sequence in context: A027039 A032009 A032027 this_sequence A057188 A128548 
               A113606
%Y A005383 Adjacent sequences: A005380 A005381 A005382 this_sequence A005384 A005385 
               A005386
%K A005383 nonn,easy
%O A005383 1,1
%A A005383 N. J. A. Sloane (njas(AT)research.att.com).
%E A005383 More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Jan 18 
               2002

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