OFFSET
1,1
COMMENTS
a(n)=0 if n is a multiple of 3, 31, 37, 41, 43, 53, 67, 71, 79, or 83. - Ray Chandler, Jul 30 2003
LINKS
Robert Israel, Table of n, a(n) for n = 1..2016
FORMULA
From Robert Israel, Feb 11 2023: (Start)
If n = 2^a * 5^b, a(n) = 2*10^max(a-1,b).
Otherwise a(n) = 0. (End)
EXAMPLE
a(7) = a(13) = 1001. Digit sum of 1001 = 2 and is the smallest such multiple of 7 and 13. a(17) = 100000001 = 17*5882353.
MAPLE
f:= proc(n) local a, b, c, k;
a:= padic:-ordp(n, 2);
b:= padic:-ordp(n, 5);
c:= n/(2^a*5^b);
if c = 1 then return 2*10^max(a-1, b) fi;
k:= traperror(NumberTheory:-ModularLog(-1, 10, c));
if k = "no solutions exist" then 0
else 10^max(a, b) * (1 + 10^k)
fi
end proc:
map(f, [$1..50]); # Robert Israel, Feb 11 2023
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Apr 01 2002
EXTENSIONS
More terms from Ray Chandler, Jul 30 2003
STATUS
approved