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 A101871 Number of Abelian groups of order 2n+1. 4
 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 3, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 3, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 LINKS Table of n, a(n) for n=0..104. FORMULA From Amiram Eldar, Sep 23 2023: (Start) a(n) = A000688(2*n+1) = A000688(4*n+2). Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 2 * A048651 * A021002 = 1.32545452721253858057... . (End) MATHEMATICA a[n_] := FiniteAbelianGroupCount[2*n + 1]; Array[a, 100, 0] (* Amiram Eldar, Sep 23 2023 *) CROSSREFS Bisection of A000688. Cf. A021002, A048651. Sequence in context: A333355 A354523 A116531 * A101875 A081387 A261795 Adjacent sequences: A101868 A101869 A101870 * A101872 A101873 A101874 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Jan 28 2005 EXTENSIONS More terms from Joshua Zucker, May 10 2006 STATUS approved

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Last modified December 1 14:40 EST 2023. Contains 367476 sequences. (Running on oeis4.)