This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A125844 a(n) = the smallest positive integer which does not occur earlier in the sequence and which is coprime to the n-th composite integer. 0
 1, 5, 3, 2, 7, 11, 9, 4, 13, 17, 19, 8, 15, 23, 6, 21, 10, 25, 29, 27, 14, 31, 12, 35, 33, 16, 37, 41, 39, 22, 43, 47, 18, 49, 20, 45, 53, 24, 51, 26, 55, 59, 57, 32, 61, 28, 65, 63, 34, 67, 71, 69, 38, 73, 30, 77, 79, 40, 75, 83, 36, 81, 44, 85, 89, 46, 87, 50, 91, 42, 95, 93 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This sequence is a permutation of the positive integers. LINKS EXAMPLE The positive integers which do not occur among the first 6 terms of the sequence are 4,6,8,9,10,12,... Of these integers, 9 is the smallest that is coprime to 14, the 7th composite. So a(7) = 9. MATHEMATICA f[l_List] := Block[{n = Length[l] + 1, c = 1, k = n}, While[k > 0, c++; While[PrimeQ[c], c++ ]; k--; ]; k = 1; While[MemberQ[l, k] || GCD[k, c] > 1, k++ ]; Append[l, k]]; Nest[f, {}, 75] (*Chandler*) CROSSREFS Cf. A002808. Sequence in context: A009661 A023576 A271523 * A171025 A222362 A176524 Adjacent sequences:  A125841 A125842 A125843 * A125845 A125846 A125847 KEYWORD nonn AUTHOR Leroy Quet, Feb 03 2007 EXTENSIONS Extended by Ray Chandler, Feb 07 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.

Last modified October 22 14:53 EDT 2018. Contains 316490 sequences. (Running on oeis4.)