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A053315
a(n) contains n digits (either '4' or '5') and is divisible by 2^n.
1
4, 44, 544, 4544, 44544, 444544, 4444544, 54444544, 454444544, 5454444544, 45454444544, 545454444544, 5545454444544, 55545454444544, 555545454444544, 4555545454444544, 44555545454444544, 544555545454444544
OFFSET
1,1
LINKS
FORMULA
a(n) = a(n-1) + 10^(n-1)*(4 + (a(n-1)/2^(n-1) mod 2)), i.e., a(n) ends with a(n-1); if (n-1)-th term is divisible by 2^n then n-th term begins with a 4, if not then n-th term begins with a 5.
MAPLE
A[1]:= 4:
for n from 2 to 100 do
if A[n-1] mod 2^n = 0 then A[n]:= A[n-1]+4*10^(n-1)
else A[n]:= A[n-1]+5*10^(n-1)
fi
od:
seq(A[i], i=1..100); # Robert Israel, Oct 27 2019
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Henry Bottomley, Mar 06 2000
EXTENSIONS
Formula corrected by Robert Israel, Oct 27 2019
STATUS
approved