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 A231344 Number of morphisms in full subcategories of Set spanned by {{}, {1}, {1, 2}, ..., {1, 2, ..., n}}. 1
 0, 1, 3, 11, 60, 499, 5705, 82207, 1419768, 28501125, 651233671, 16676686707, 472883844004, 14705395791319, 497538872883741, 18193397941038751, 714950006521386992, 30046260016074301961, 1344648068888240941035 (list; graph; refs; listen; history; text; internal format)
 OFFSET -1,3 COMMENTS For any natural number k, consider the set X_k={1,2,...,k}; in particular X_0 is empty. For any natural number n, let S_n be the full subcategory of Set spanned by the objects X_0, X_1,...,X_n. Then S_n has some number of morphisms, #S_n. When n=-1, we consider S_n to be empty. Our sequence is #S_{-1}, #S_0, #S_1, #S_2,.... LINKS Robert G. Wilson v, Table of n, a(n) for n = -1..386 FORMULA a(n)=sum_{0<=i,j<=n}i^j, where 0^0=1. EXAMPLE For n=2, we have 0^0+0^1+0^2+1^0+1^1+1^2+2^0+2^1+2^2=11. MATHEMATICA a[n_] := 1 + Sum[i^j, {j, 0, n}, {i, n}]; a[-1] = 0; Array[a, 19, -1] (* Robert G. Wilson v, Feb 18 2014 *) PROG (PARI) a(n)=sum(i=0, n, sum(j=0, n, i^j)) \\ - M. F. Hasler, Nov 08 2013 CROSSREFS Sequence in context: A075201 A136440 A303871 * A007146 A076475 A125556 Adjacent sequences:  A231341 A231342 A231343 * A231345 A231346 A231347 KEYWORD nonn AUTHOR David Spivak, Nov 07 2013 EXTENSIONS More terms from M. F. Hasler, Nov 08 2013 STATUS approved

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Last modified January 18 09:26 EST 2022. Contains 350454 sequences. (Running on oeis4.)