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 A325403 Number of permutations of the multiset of prime factors of 2n whose first part is not 2. 2
 0, 0, 1, 0, 1, 1, 1, 0, 2, 1, 1, 1, 1, 1, 4, 0, 1, 3, 1, 1, 4, 1, 1, 1, 2, 1, 3, 1, 1, 6, 1, 0, 4, 1, 4, 4, 1, 1, 4, 1, 1, 6, 1, 1, 9, 1, 1, 1, 2, 3, 4, 1, 1, 6, 4, 1, 4, 1, 1, 8, 1, 1, 9, 0, 4, 6, 1, 1, 4, 6, 1, 5, 1, 1, 9, 1, 4, 6, 1, 1, 4, 1, 1, 8, 4, 1, 4, 1, 1, 18, 4, 1, 4, 1, 4, 1, 1, 3, 9, 4, 1, 6, 1, 1, 18 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,9 LINKS Antti Karttunen, Table of n, a(n) for n = 1..20000 FORMULA a(n) = A008480(2n) - A008480(n) = A325392(2n). EXAMPLE The a(60) = 8 permutations of {2,2,2,3,5} whose first part is not 2: 3 2 2 2 5 3 2 2 5 2 3 2 5 2 2 3 5 2 2 2 5 2 2 2 3 5 2 2 3 2 5 2 3 2 2 5 3 2 2 2 MATHEMATICA Table[Length[Select[Permutations[Flatten[Table@@@FactorInteger[2*n]]], First[#]!=2&]], {n, 100}] PROG (PARI) A008480(n) = {my(sig=factor(n)[, 2]); vecsum(sig)!/factorback(apply(k->k!, sig))}; \\ After code in A008480 A325403(n) = (A008480(n+n)-A008480(n)); \\ _Antti Karttunen_, Dec 06 2021 CROSSREFS Cf. A008480, A056239, A112798, A325327, A325362, A325364, A325367, A325390, A325392, A325407. Sequence in context: A218220 A247487 A010248 * A132068 A173441 A326851 Adjacent sequences: A325400 A325401 A325402 * A325404 A325405 A325406 KEYWORD nonn AUTHOR _Gus Wiseman_, May 02 2019 EXTENSIONS Data section extended up to 105 terms by _Antti Karttunen_, Dec 06 2021 STATUS approved

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Last modified March 2 02:30 EST 2024. Contains 370447 sequences. (Running on oeis4.)