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 A046524 Number of coverings of Klein bottle with n lists. 3
 1, 3, 2, 5, 2, 7, 2, 8, 3, 8, 2, 13, 2, 9, 4, 13, 2, 14, 2, 16, 4, 11, 2, 23, 3, 12, 4, 19, 2, 22, 2, 22, 4, 14, 4, 30, 2, 15, 4, 30, 2, 26, 2, 25, 6, 17, 2, 41, 3, 23, 4, 28, 2, 30, 4, 37, 4, 20, 2, 50, 2, 21, 6, 39, 4, 34, 2, 34, 4, 34, 2, 59, 2, 24, 6, 37, 4, 38, 2, 56, 5, 26, 2, 62, 4, 27, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS T. D. Noe, Table of n, a(n) for n=1..1000 V. A. Liskovets and A. Mednykh, Number of non-orientable coverings of the Klein bottle A. D. Mednykh, On the number of subgroups in the fundamental group of a closed surface, Commun. in Algebra, 16, No 10 (1988), 2137-2148. FORMULA a(n)=d(n) (the number of divisors) for odd n. a(n)=[3d(n)+sigma(n/2)-d(n/2)]/2 for even n where d(n) is the number and sigma(n) the sum of divisors of n (A000005 and A000203). Inverse Moebius transform of 1, 2, 1, 2, 1, 3, 1, 3, 1, 4, 1, 4, 1, 5, 1, 5, 1, 6, 1, 6, 1, 7, 1, 7, ... . G.f.: Sum_{n>1} x^n*(1+2*x^n-x^(4*n)-x^(5*n))/(1+x^(2*n))/(1-x^(2*n))^2. - Vladeta Jovovic, Feb 03 2003 MAPLE with(numtheory); A046524:=n->`if`(type(n/2, integer), (3*tau(n) + sigma(n/2) - tau(n/2))/2, tau(n)); seq(A046524(n), n=1..100); # Wesley Ivan Hurt, Feb 14 2014 MATHEMATICA kb[n_]:=If[OddQ[n], DivisorSigma[0, n], (3DivisorSigma[0, n]+ DivisorSigma[ 1, n/2]- DivisorSigma[0, n/2])/2]; Array[kb, 90] (* Harvey P. Dale, Oct 08 2011 *) PROG (Sage) def A046524(n) :     f = lambda n : 1 if n % 2 == 1 else (n+7)//4     return add(f(d) for d in divisors(n)) [A046524(n) for n in (1..87)] # Peter Luschny, Jul 23 2012 CROSSREFS Cf. A027842, A027844, A000005, A000203, A069733, A069734, A069735. Sequence in context: A069735 A274457 A328579 * A086571 A133945 A124219 Adjacent sequences:  A046521 A046522 A046523 * A046525 A046526 A046527 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from Vladeta Jovovic, Feb 03 2003 STATUS approved

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Last modified June 20 21:01 EDT 2021. Contains 345236 sequences. (Running on oeis4.)