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A308476
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a(1) = 1; a(n) = Sum_{k=1..n-1, gcd(n,k) = 1} Stirling2(n,k)*a(k).
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1
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1, 1, 4, 25, 366, 5491, 176569, 5332097, 276268942, 13470365431, 1135683784753, 75066413338423, 9256260956838520, 918768523598548169, 140268128758724744770, 18398287904991375995745, 3879391299475140314514162, 594721341754741064012714341
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OFFSET
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1,3
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LINKS
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MAPLE
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a := proc(n) local j; option remember;
if n = 1 then 1;
else add(`if`(gcd(n, j) = 1, Stirling2(n, j)*a(j), 0), j = 1 .. n - 1);
end if; end proc;
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MATHEMATICA
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a[n_] := Sum[If[GCD[n, k] == 1, StirlingS2[n, k] a[k], 0], {k, 1, n - 1}]; a[1] = 1; Table[a[n], {n, 1, 18}]
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PROG
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(Sage)
@CachedFunction
def a(n):
if n==1: return 1
else: return sum( stirling_number2(n, j)*a(j) if gcd(n, j)==1 else 0 for j in (1..n-1) )
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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