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A128204
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a(0) = 0; a(n) = a(n-1) - (2n-1) if that number is positive and not already in the sequence, otherwise a(n) = a(n-1) + (2n-1).
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2
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0, 1, 4, 9, 2, 11, 22, 35, 20, 3, 22, 43, 66, 41, 14, 43, 12, 45, 10, 47, 8, 49, 6, 51, 98, 147, 96, 149, 94, 37, 96, 157, 220, 155, 88, 19, 90, 17, 92, 15, 94, 13, 96, 181, 268, 179, 270, 177, 82, 179, 80, 181, 78, 183, 76, 185, 74, 187, 72, 189, 70, 191, 68, 193, 320
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OFFSET
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0,3
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COMMENTS
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'Recamán transform' (see A005132) of the odd numbers.
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LINKS
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EXAMPLE
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Consider n=7. We have a(6)=22 and try to subtract 13, the 7th odd number. The result, 9, is certainly positive, but we cannot use it because 9 is already in the sequence. So we must add 13 instead, getting a(7) = 22 + 13 = 35.
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PROG
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(PARI) A128204(N, s/*=1 to print all terms*/)={my(a=0, u=0); for( n=1, N, s&print1(a", "); u=bitor(u, 2^a+=if(a<2*n || bittest(u, a+1-2*n), 2*n-1, 1-2*n))); a} \\ M. F. Hasler, Mar 07 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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