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%I #22 Sep 08 2022 08:45:06
%S 2,3,4,5,6,8,10,11,13,14,18,19,21,25,30,31,36,41,43,44,46,47,48,50,52,
%T 53,58,59,60,62,63,66,68,70,73,74,75,78,79,80,81,83,85,90,93,99,100,
%U 101,106,112,114,116,117,120,124,126,127,129,130,131,132,137,138,140,145,147,149
%N Numbers n such that prime(n) + prime(n+1) - 1 is prime.
%H Vincenzo Librandi, <a href="/A072666/b072666.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = pi(A072667(n)) = A000720(A072667(n)). - _Zak Seidov_, Dec 08 2014
%p N:= 10^4: # to get all terms n such that prime(n+1) <= N
%p Primes:= select(isprime,[2,seq(2*i+1,i=1..floor(N/2))]):
%p PP:= Primes[1..-2]+Primes[2..-1]:
%p select(t -> isprime(PP[t]-1), [$1..nops(PP)]); # _Robert Israel_, Dec 11 2014
%t Select[Range[200], PrimeQ[Prime[#]+Prime[#+1]-1] &] (* _Harvey P. Dale_, Dec 16 2010 *)
%o (Magma) [n: n in [1..200] | IsPrime(NthPrime(n) + NthPrime(n+1)-1)] // _Vincenzo Librandi_, Aug 26 2012
%Y Cf. A000720, A072667, A072669, A177017.
%K nonn
%O 1,1
%A Herman H. Rosenfeld (herm3(AT)pacbell.net), Aug 12 2002
%E Definition clarified by _Robert Israel_, Dec 11 2014
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