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Irregular triangle in which row n has all primes q such that prime(n)*q is a base-2 Fermat pseudoprime.
5

%I #16 Mar 28 2021 07:03:59

%S 31,257,73,89,683,113,11,151,331,73,109,61681,127,337,5419,178481,

%T 2796203,157,1613,233,1103,2089,3033169,1321,20857,599479,281,86171,

%U 122921,19,37,109,433,38737,2731,8191,121369,22366891,13367,164511353,8831418697,23,353,397,683,2113,2931542417

%N Irregular triangle in which row n has all primes q such that prime(n)*q is a base-2 Fermat pseudoprime.

%C The length of row n is A085014(n). The smallest and largest primes in row n are A085012(n) and A085019(n).

%D See A085012.

%H Amiram Eldar, <a href="/A180471/b180471.txt">Table of n, a(n) for n = 5..3424</a>

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>

%e The irregular triangle begins

%e 31

%e none

%e 257

%e 73

%e 89, 683

%e 113

%e 11, 151, 331

%e 73, 109

%e 61681

%t Flatten[Table[p=Prime[n]; q=Transpose[FactorInteger[2^(p-1)-1]][[1]]; cnt={}; Do[If[PowerMod[2, p*q[[i]]-1, p*q[[i]]]==1, AppendTo[cnt,q[[i]]]], {i,Length[q]}]; cnt, {n,5,50}]]

%Y Cf. A085012, A085014, A085019.

%K nonn,tabf

%O 5,1

%A _T. D. Noe_, Jan 19 2011