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A116533 revision #6

A116533
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.
14
1, 2, 4, 3, 6, 5, 10, 9, 8, 7, 14, 13, 26, 25, 24, 23, 46, 45, 44, 43, 86, 85, 84, 83, 166, 165, 164, 163, 326, 325, 324, 323, 322, 321, 320, 319, 318, 317, 634, 633, 632, 631, 1262, 1261, 1260, 1259, 2518, 2517, 2516, 2515, 2514, 2513, 2512, 2511, 2510, 2509, 2508
OFFSET
1,2
COMMENTS
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
MAPLE
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
CROSSREFS
KEYWORD
nonn
AUTHOR
Rodolfo Kurchan, Mar 26 2006
EXTENSIONS
More terms from Emeric Deutsch, Apr 02 2006
STATUS
editing