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A180074 Squarefree semiprimes s=p*q, p<q, such that 2^s mod s = 2^p. 1
6, 10, 14, 15, 21, 22, 26, 33, 34, 38, 39, 46, 51, 57, 58, 62, 65, 69, 74, 82, 85, 86, 87, 93, 94, 106, 111, 118, 122, 123, 129, 133, 134, 141, 142, 145, 146, 158, 159, 166, 177, 178, 183, 185, 194, 201, 202, 205, 206, 213, 214, 217, 218, 219, 226, 237 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It may seem that this is a subsequence of A162730, but it is not so, 131801 being the first counterexample. - Michel Marcus, Sep 19 2018

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

f[n_]:=With[{f=FactorInteger[n][[All, 1]]}, PowerMod[ 2, Times@@f, Times@@f] == 2^f[[1]]]; Select[Range[250], PrimeOmega[#]==2&&SquareFreeQ[#]&&f[#]&] (* Harvey P. Dale, Jun 06 2017 *)

PROG

(PARI) isok(n) = {if ((bigomega(n) == 2) && (omega(n) == 2), my(p = factor(n)[1, 1]); lift(Mod(2, n)^n) == 2^p); } \\ Michel Marcus, Sep 19 2018

CROSSREFS

Cf. A006881, A015910, A162730, A179976.

Sequence in context: A201514 A201464 A162730 * A338905 A093772 A046400

Adjacent sequences:  A180071 A180072 A180073 * A180075 A180076 A180077

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jan 14 2011

EXTENSIONS

Definition and terms corrected by R. J. Mathar, Jan 14 2011

STATUS

approved

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Last modified April 20 01:36 EDT 2021. Contains 343117 sequences. (Running on oeis4.)