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%I #15 Apr 03 2023 10:36:09
%S 3,29,53,113,131,173,191,233,239,251,281,293,419,431,443,491,593,641,
%T 653,659,683,743,761,809,911,953,1013,1049,1103,1223,1289,1499,1559,
%U 1583,1601,1733,1973,2003,2069,2129,2141,2273,2339,2351,2393,2399,2543
%N Initial primes of Cunningham chains of first type with length exactly 2. Primes in A059453 which survive as primes only one "2p-1 iteration", forming chains of exactly 2 terms.
%H Harvey P. Dale, <a href="/A059761/b059761.txt">Table of n, a(n) for n = 1..1000</a>
%H Chris Caldwell's Prime Glossary, <a href="https://t5k.org/glossary/page.php?sort=CunninghamChain">Cunningham chains</a>.
%H Warut Roonguthai, <a href="http://web.archive.org/web/20010405230842/http://ksc9.th.com/warut/cunningham.html">Yves Gallot's Proth.exe and Cunningham Chains</a>.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CunninghamChain.html">Cunningham Chain</a>
%F {(p-1)/2, p, 2p+1, 4p+3} = {composite, prime, prime, composite}
%e 53 is here because 26 and 215 are composites,53 and 107 are primes
%t ccftQ[p_]:=Boole[PrimeQ[{(p-1)/2,p,2 p+1,4 p+3}]]=={0,1,1,0}; Select[ Prime[ Range[400]],ccftQ] (* _Harvey P. Dale_, Jun 19 2021 *)
%Y A023272, A023302, A023330, A005384, A005385, A059452-A059455, A007700.
%K nonn
%O 1,1
%A _Labos Elemer_, Feb 20 2001
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