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A179707 Semiprimes p*q such that 2^p (mod q) == 2^q (mod p). 3
4, 9, 25, 49, 121, 169, 289, 341, 361, 529, 731, 841, 961, 1333, 1369, 1387, 1681, 1727, 1849, 2047, 2209, 2701, 2809, 3277, 3481, 3503, 3721, 3763, 4033, 4369, 4489, 4681, 5041, 5329, 5461, 6241, 6889, 7921, 7957, 8321, 9409, 9509, 10201, 10261, 10609, 10669, 11449, 11881 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
The square of every prime is here, as are the semiprimes in A179839.
LINKS
EXAMPLE
341 is a term because 341=11*31 and 2^11 mod 31 = 2^31 mod 11.
MATHEMATICA
fQ[n_] := Block[{fi = Flatten[ Table[ First@ #, {Last@ #}] & /@ FactorInteger@ n]}, Length@ fi == 2 && PowerMod[2, fi[[2]], fi[[1]]] == PowerMod[2, fi[[1]], fi[[2]]]]; Select[ Range@ 12000, fQ]
With[{nn=50}, Take[Union[Times@@@Select[Tuples[Prime[Range[2nn]], 2], PowerMod[ 2, #[[1]], #[[2]]]==PowerMod[2, #[[2]], #[[1]]]&]], nn]] (* Harvey P. Dale, Sep 03 2015 *)
CROSSREFS
Sequence in context: A082180 A246131 A068999 * A247078 A077438 A350343
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified February 24 04:32 EST 2024. Contains 370288 sequences. (Running on oeis4.)