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Intersection of A001567 and A212502.
2

%I #26 Jul 24 2021 05:39:55

%S 4033,6601,8321,15841,25761,29341,41041,46657,75361,115921,162401,

%T 172081,252601,294409,314821,332949,401401,410041,488881,530881,

%U 552721,642001,721801,873181,934021,1004653,1207361,1461241,1876393,1909001,2081713,2085301,2113921

%N Intersection of A001567 and A212502.

%C Only 1 (mod 4) numbers have been found.

%H Amiram Eldar, <a href="/A212601/b212601.txt">Table of n, a(n) for n = 1..10000</a>

%t t[n_] := Which[Mod[n, 4] == 3, n + 1, Mod[n, 4] == 1, n - 1, True, n]; Select[1 + Range[99000], PowerMod[2, # - 1, #] == 1 && !PrimeQ[#] && Im[PowerMod[1 + 2I, t[#], #]] == 0 &]

%Y Cf. A201629.

%Y Cf. A001567 (pseudoprimes to base 2).

%Y Cf. A212502 (pseudoprimes to base 1+2i).

%K nonn

%O 1,1

%A _José María Grau Ribas_, May 22 2012