A147553 Numbers k such that k^2 divides k.k where dot "." means concatenation.
1, 143, 142857143, 142857142857143, 142857142857142857143, 142857142857142857142857143, 142857142857142857142857142857143, 142857142857142857142857142857142857143
Offset: 1
Examples
143*143|143.143 (143143/(143*143)=7) so 143 is in the sequence.
Links
- Robert Israel, Table of n, a(n) for n = 1..167
- Index entries for linear recurrences with constant coefficients, signature (1000001,-1000000).
Programs
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Maple
1, seq((10^(6*n-3)+1)/7, n=1..20); # Robert Israel, Sep 26 2016
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Mathematica
a[0]=1;a[n_]:=(10^(6n-3)+1)/7;Table[a[k],{k,0,8}] Do[d=Divisors[10^i+1];s=Select[d,Length[IntegerDigits[#]]==i&];If[Length[s]>0,Do[Print[s[[j]]],{j,Length[s]}]],{i,69}] (* Hans Havermann, May 31 2014 *) LinearRecurrence[{1000001,-1000000},{1,143,142857143},20] (* Harvey P. Dale, Apr 02 2018 *)
Comments