This site is supported by donations to The OEIS Foundation.

 Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS". Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A128204 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). 2
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 'Recamán transform' (see A005132) of the odd numbers. LINKS Nick Hobson, Python program for this sequence EXAMPLE 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. PROG (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 CROSSREFS Cf. A005132, A053461, A064365, A123483. Sequence in context: A203816 A070437 A238324 * A079049 A114578 A135044 Adjacent sequences:  A128201 A128202 A128203 * A128205 A128206 A128207 KEYWORD easy,nonn AUTHOR Nick Hobson (nickh(AT)qbyte.org), Feb 19 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.