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 A069925 a(n) = phi(2^n+1)/(2*n). 0
 1, 1, 1, 2, 2, 4, 6, 16, 18, 40, 62, 160, 210, 448, 660, 2048, 2570, 5184, 9198, 24672, 32508, 76032, 121574, 344064, 405000, 1005888, 1569780, 4511520, 6066336, 12672000, 23091222, 67004160, 85342752, 200422656, 289531200, 892477440 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Number of primitive self-reciprocal polynomials of degree 2*n over GF(2). - Joerg Arndt, Jul 04 2012 LINKS Joerg Arndt, Matters Computational (The Fxtbook), section 40.8 "Self-reciprocal polynomials", pp. 846-484. Helmut Meyn and Werner Götz, Self-reciprocal Polynomials Over Finite Fields, Séminaire Lotharingien de Combinatoire, B21d, pp.82-90, 1989. FORMULA a(n) = phi(2^n+1)/(2*n). MATHEMATICA Table[EulerPhi[2^n+1]/(2n), {n, 50}] (* Harvey P. Dale, Nov 15 2011 *) PROG (PARI) a(n) = eulerphi(2^n+1)/(2*n); /* Joerg Arndt, Jul 04 2012 */ CROSSREFS Cf. A011260 (degree-n primitive polynomials). Cf. A000048 (degree-2*n irreducible self-reciprocal polynomials). Sequence in context: A116637 A153961 A134041 * A227315 A080611 A171421 Adjacent sequences:  A069922 A069923 A069924 * A069926 A069927 A069928 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Apr 25 2002 STATUS approved

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Last modified October 14 05:08 EDT 2019. Contains 327995 sequences. (Running on oeis4.)