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A228007 The largest n-digit number whose first k digits are divisible by k^2 for k = 1..n. 0

%I

%S 9,96,963,9632,96325,963252,6480005

%N The largest n-digit number whose first k digits are divisible by k^2 for k = 1..n.

%C There are 7 terms in the sequence and the 7-digit number 6480005 is the largest number to satisfy the requirements.

%e There are nine one-digit numbers divisible by 1 and the largest is 9, so a(1)=9.

%e For two-digit numbers, the second digit must make it divisible by 2^2, which gives 96 as the largest to satisfy the requirement, so a(2)=96.

%t a = Table[j, {j, 9}]; r = 2; t = {}; While[! a == {}, n = Length[a]; nmax = Last[a]; k = 1; b = {}; While[! k > n, z0 = a[[k]]; Do[z = 10*z0 + j; If[Mod[z, r*r] == 0, b = Append[b, z]], {j, 0, 9}]; k++]; AppendTo[t, nmax]; a = b; r++]; t

%Y Cf. A079042.

%K nonn,base,fini,full

%O 1,1

%A _Shyam Sunder Gupta_, Aug 08 2013

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Last modified December 4 19:40 EST 2021. Contains 349526 sequences. (Running on oeis4.)