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A048941 a(n) is twice the coefficient of 1 in the fundamental unit of Q(sqrt(n)) where n ranges over the nonsquare numbers A000037. 1
2, 4, 1, 10, 16, 2, 6, 20, 4, 3, 30, 8, 8, 2, 340, 1, 5, 394, 48, 10, 10, 4, 16, 5, 22, 3040, 2, 46, 70, 12, 12, 74, 50, 6, 64, 26, 6964, 20, 1, 48670, 96, 4, 2, 100, 3, 7, 10, 178, 30, 302, 198, 1060, 8, 39, 126, 16, 16, 130, 97684, 8, 25, 502, 6960, 2, 2136, 86, 4, 340, 9, 106, 160, 1, 18, 164, 5, 9, 20810 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..77.

S. R. Finch, Class number theory

Eric Weisstein's World of Mathematics, Fundamental Unit.

MATHEMATICA

nonSquares = Select[Range[72], !IntegerQ[Sqrt[#]]& ]; 2*NumberFieldFundamentalUnits[Sqrt[#]][[1, 2, 1]] & /@ nonSquares (* Jean-François Alcover, Nov 09 2012 *)

PROG

(PARI) for(n=1, 30, if(!issquare(n), print1(abs(2*polcoeff(lift(bnfinit(x^2-n).tufu[2]), 0)), ", "))) /* Ralf Stephan, Sep 18 2013 */

CROSSREFS

Cf. A048942.

Sequence in context: A114848 A135330 A135328 * A246188 A135333 A124503

Adjacent sequences:  A048938 A048939 A048940 * A048942 A048943 A048944

KEYWORD

nonn

AUTHOR

Eric W. Weisstein

EXTENSIONS

Changes after re-computation with Mathematica : a(14) = 2 (instead of 34), a(16) = 1 (4), a(22) = 4 (52), a(27) = 2 (6), a(39) = 1 (7), a(42) = 4 (14), a(43) = 2 (14), a(45) = 3 (36), a(47) = 10 (970), a(64) = 2 (34). Data modified by Jean-François Alcover, Dec 12 2012

STATUS

approved

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Last modified January 21 19:08 EST 2019. Contains 319350 sequences. (Running on oeis4.)