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A293394
Numbers k such that (2*k-1)*(2^((k-1)/4)) == 1 (mod k).
7
1, 17, 41, 97, 137, 193, 241, 313, 401, 409, 433, 449, 457, 521, 569, 641, 673, 761, 769, 809, 857, 929, 953, 977, 1009, 1129, 1297, 1321, 1361, 1409, 1489, 1657, 1697, 1873, 1993, 2017, 2081, 2137, 2153, 2161
OFFSET
1,2
COMMENTS
It appears that many elements of this sequence are prime. The first "pseudoprime" in this sequence is 74665.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[1, 3001, 4], #==1 || Mod[-PowerMod[#-2, (#-1)/4, #], #]==1&] (* Jean-François Alcover, Nov 18 2018 *)
PROG
(PARI) is(n)=n%4==1 && (2*n-1)*Mod(2, n)^(n>>2)==1 \\ Charles R Greathouse IV, Nov 09 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonas Kaiser, Nov 09 2017
STATUS
approved