A328510 Smallest number whose divisors have n non-singleton runs.
1, 2, 20, 90, 630, 1260, 3780, 21420, 41580, 128520, 270270, 554400, 706860, 1413720, 2042040, 4324320, 4084080, 9189180, 6126120, 43825320, 12252240, 18378360, 82162080, 36756720, 85765680, 73513440, 183783600, 306306000, 257297040, 563603040, 514594080
Offset: 0
Keywords
Examples
The sequence of terms together with their non-singleton runs of divisors begins:
1: {}
2: {{1,2}}
20: {{1,2},{4,5}}
90: {{1,2,3},{5,6},{9,10}}
630: {{1,2,3},{5,6,7},{9,10},{14,15}}
Links
- Giovanni Resta, Table of n, a(n) for n = 0..54
Crossrefs
Equal {1} followed by the positions of first appearances in A328511 (times 2).
The longest run of divisors of n has length A055874.
Numbers whose divisors have no non-singleton runs are A005408.
The number of successive pairs of divisors of n is A129308(n).
The number of singleton runs of divisors is A132881.
Programs
-
Mathematica
dv=Table[Length[DeleteCases[Length/@Split[Divisors[n],#2==#1+1&],1]],{n,1000}]; Table[Position[dv,i][[1,1]],{i,Union[dv]}]
Extensions
Offset changed to 0 and a(10)-a(30) added by Giovanni Resta, Oct 25 2019