login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A126638 a(n) is larger than a(n-1), not prime and coprime to a(n-1) and a(n-2). 2
4, 9, 25, 26, 27, 35, 38, 39, 49, 50, 51, 77, 80, 81, 91, 92, 93, 95, 98, 99, 115, 116, 117, 119, 121, 122, 123, 125, 128, 129, 133, 134, 135, 143, 146, 147, 155, 158, 159, 161, 164, 165, 169, 172, 175, 177, 178, 185, 187, 188, 189, 205, 206, 207, 209, 212, 213 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
a(7) = 38 because it is the next composite number larger than 35 (a(6)) that shares no factors in common with 35 and 27 (a(5)).
MAPLE
with(numtheory); i:=4; j:=9; k:=10; while(k < 100) do while(order(k, i) = FAIL or order(k, j) = FAIL or isprime(k)) do k:=k+1; end do; print(k); i:= j; j:=k; k:=k+1; end do;
MATHEMATICA
f[l_List] := Block[{k = l[[ -1]] + 1}, While[PrimeQ[k] || GCD[k, l[[ -1]]*l[[ -2]]] > 1, k++ ]; Append[l, k]]; Nest[f, {4, 9}, 56] (* Ray Chandler, Feb 14 2007 *)
nxt[{a_, b_}]:=Module[{k=b+1}, While[PrimeQ[k]||!CoprimeQ[a, k] || !CoprimeQ[ b, k], k++]; {b, k}]; NestList[nxt, {4, 9}, 60][[All, 1]] (* Harvey P. Dale, Aug 31 2021 *)
CROSSREFS
Cf. A051884.
Sequence in context: A251544 A175119 A093867 * A340640 A073045 A045967
KEYWORD
nonn
AUTHOR
Ben Paul Thurston, Feb 08 2007
EXTENSIONS
Extended by Ray Chandler, Feb 14 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 14 18:28 EDT 2024. Contains 371667 sequences. (Running on oeis4.)