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 A359808 a(n) is the least prime factor of the alternating factorial n! - (n-1)! + (n-2)! - ... 1! for n > 2; a(1) = a(2) = 1. 2
 1, 1, 5, 19, 101, 619, 4421, 35899, 79, 3301819, 13, 29, 47, 23, 1226280710981, 53, 47, 2683, 115578717622022981, 8969, 113, 79, 85439, 12203, 59, 1657, 127, 61, 661, 47, 173183, 1117, 83, 4729, 37, 103, 2858548279, 59, 67, 431, 32656499591185747972776747396512425885838364422981 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n) is the least prime factor of A005165(n) (unless A005165(n) = 1, in which case a(n) = 1). a(n) = A005165(n) iff n is a term in A001272 or n < 2. LINKS Jon E. Schoenfield, Table of n, a(n) for n = 1..149 Eric Weisstein's World of Mathematics, Alternating Factorial FORMULA a(n) = A020639(A005165). MAPLE b:= proc(n) option remember; `if`(n=0, 0, n!-b(n-1)) end: a:= n-> `if`(n<3, 1, min(numtheory[factorset](b(n)))): seq(a(n), n=1..41); # Alois P. Heinz, Jan 13 2023 MATHEMATICA a[n_] := FactorInteger[AlternatingFactorial[n]][[1, 1]]; Table[a[n], {n, 1, 41}] (* Jean-François Alcover, Jan 24 2023 *) CROSSREFS Cf. A001272, A005165, A020639. Sequence in context: A146144 A162292 A321875 * A005165 A071828 A280067 Adjacent sequences: A359805 A359806 A359807 * A359809 A359810 A359811 KEYWORD nonn AUTHOR Jon E. Schoenfield, Jan 13 2023 STATUS approved

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Last modified May 30 07:51 EDT 2023. Contains 363050 sequences. (Running on oeis4.)