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 A113950 Number of n-fold branched coverings of the Klein bottle with r cyclic branch points (n,r>=1); array read by downward antidiagonals. 2
 1, 1, 0, 1, 4, 5, 1, 0, 13, 0, 1, 4, 23, 104, 44, 1, 0, 49, 0, 1256, 0, 1, 4, 95, 2720, 27344, 30608, 1266, 1, 0, 193, 0, 666656, 0, 1071540, 0, 1, 4, 383, 93824, 15911744, 415444544, 743214744 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS The odd bisection of the first column is A113948. REFERENCES J. H. Kwak, A. Mednykh and V. Liskovets, Enumeration of branched coverings of nonorientable surfaces with cyclic branch points, SIAM J. Discrete Math., Vol. 19, No. 2 (2005), 388-398. LINKS FORMULA E.g. for n=7 and r>=1, a(7, r)=2*720^r+(-1)^r*2*120^r+2*48^r+(-1)^r*36^r+6^r (more generally, a(7, r, h)=7^(h-2)*(2*720^m+(-1)^r*2*120^m+2*48^m+(-1)^r*36^m+6^r) for 7-sheeted coverings of the non-orientable surface of genus h>=1, where m=h+r-2). EXAMPLE The array begins: 1 1 1 1 1 1 ... 0 4 0 4 0 4 ... 5 13 23 49 95 193 ... 0 104 0 2720 0 93824 ... CROSSREFS Cf. A113948, A113949. Sequence in context: A122753 A016714 A211799 * A269944 A121906 A028360 Adjacent sequences:  A113947 A113948 A113949 * A113951 A113952 A113953 KEYWORD nonn,tabl AUTHOR Valery A. Liskovets, Nov 10 2005 STATUS approved

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Last modified December 12 12:30 EST 2019. Contains 329958 sequences. (Running on oeis4.)