|
%I #9 Jan 17 2022 13:41:10
%S 2,3,5,3,5,13,17,19,19,29,23,31,29,31,43,19,59,53,61,59,59,79,67,83,
%T 61,89,103,101,109,113,109,97,131,109,149,137,149,127,163,139,149,109,
%U 149,163,197,191,197,223,227,229,211,239,241,241,223,241,269,233,271,269
%N Largest prime p < prime(n) such that prime(n) + 2 * p is a prime.
%H Reinhard Zumkeller, <a href="/A114230/b114230.txt">Table of n, a(n) for n = 2..10000</a>
%e prime(2)=3, 3+2*2=7 is prime, so a(2)=2;
%e prime(3)=5, 5+2*3=11 is prime, so a(3)=3;
%e ...
%e prime(11)=31, 31+2*29=89 is prime, so a(11)=29.
%t Table[p1 = Prime[n1]; n2 = n1 - 1; p2 = Prime[n2]; While[cp = p1 + 2*p2; ! PrimeQ[cp], n2--; If[n2 == 0, Print[n1]]; p2 = Prime[n2]]; p2, {n1, 2, 201}]
%t lp[n_]:=Module[{p=NextPrime[n,-1]},While[!PrimeQ[n+2p],p=NextPrime[p,-1]];p]; Table[lp[p],{p,Prime[Range[2,70]]}] (* _Harvey P. Dale_, Jan 17 2022 *)
%o (Haskell)
%o a114230 n = head [p | let q = a000040 n,
%o p <- reverse $ takeWhile (< q) a000040_list,
%o a010051 (q + 2 * p) == 1]
%o -- _Reinhard Zumkeller_, Oct 29 2013
%Y Cf. A114227.
%Y Cf. A000040, A010051.
%K easy,nonn
%O 2,1
%A _Lei Zhou_, Nov 18 2005
%E Edited definition to conform to OEIS style. - _Reinhard Zumkeller_, Oct 29 2013
|
