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a(1)=1, a(2)=2, for n > 2 if a(n-1) is prime, then a(n) = 2*a(n-1), otherwise a(n) = a(n-1) - 1.
For n >= 3, using Wilson's theorem, a(n) = a(n-1) + (-1)^r*gcd(a(n-1), W), where W = A038507(a(n-1) - 1), and r=1 if gcd(a(n-1), W) = 1 and r=0 otherwise. - Vladimir Shevelev, Aug 07 2009
a[1]:=1: a[2]:=2: for n from 3 to 60 do if isprime(a[n-1])=true then a[n]:=2*a[n-1] else a[n]:=a[n-1]-1 fi od: seq(a[n], n=1..60); - _# _Emeric Deutsch_, Apr 02 2006
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Comment from _Vladimir Shevelev_, Aug 07 2009: For n>=3, using Wilson's theorem, a(n)=a(n-1)+ (-1)^r*gcd(a(n-1), W), where W = A038507(a(n-1)-1), and r=1 if gcd(a(n-1),W) = 1 and r=0 otherwise. - _Vladimir Shevelev_, Aug 07 2009
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Comment from Vladmir _Vladimir Shevelev (shevelev(AT)bgu.ac.il), _, Aug 07 2009: For n>=3, using Wilson's theorem, a(n)=a(n-1)+ (-1)^r*gcd(a(n-1), W), where W = A038507(a(n-1)-1), and r=1 if gcd(a(n-1),W) = 1 and r=0 otherwise.
_Rodolfo Marcelo Kurchan (rkurchan(AT)yahoo.com), _, Mar 26 2006
a[1]:=1: a[2]:=2: for n from 3 to 60 do if isprime(a[n-1])=true then a[n]:=2*a[n-1] else a[n]:=a[n-1]-1 fi od: seq(a[n], n=1..60); - _Emeric Deutsch (deutsch(AT)duke.poly.edu), _, Apr 02 2006
More terms from _Emeric Deutsch (deutsch(AT)duke.poly.edu), _, Apr 02 2006
a(1)=1, a(2)=2, for n>2 if a(n-1) is prime, then a(n)=2a2*a(n-1), otherwise a(n)=a(n-1)-1.
Comment from Vladmir Shevelev (shevelev(AT)bgu.ac.il), Aug 07 2009: For n>=3, using Wilson's theorem, a(n)=a(n-1)+ (-1)^r*gcd(a(n-1), W), where W = A038507(a(n-1)-1), and r=1 if gcd(a(n-1),W) = 1 and r=0 otherwise.
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