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A141027
a(n) = smallest number m which without its leftmost digit is equal to m/n (or 0 if no such number exists).
0
0, 15, 0, 25, 12, 35, 0, 45, 0, 11, 0, 65, 0, 75, 32, 85, 0, 95, 0, 21, 0, 0, 0, 625, 52, 0, 0, 725, 0, 31, 0, 825, 0, 0, 72, 925, 0, 0, 0, 41, 0, 0, 0, 0, 92, 0, 0, 6125, 0, 51, 0, 0, 0, 0, 0, 7125, 0, 0, 0, 61, 0, 0, 0, 8125, 0, 0, 0, 0, 0, 71, 0, 9125, 0, 0, 304, 0, 0, 0, 0, 81, 0, 0, 0
OFFSET
2,2
FORMULA
For n>10, a(n) is nonzero only if n-1 divides k*10^s for some positive integers k<=9 and s. For minimum such number k*10^s, we have a(n) = n*k*10^s/(n-1). - Max Alekseyev, Apr 13 2009
EXAMPLE
a(7) = 35: 35/7 = 5 = 35 with leftmost digit deleted.
PROG
(PARI) { a(n) = if(n<=10, return([0, 0, 15, 0, 25, 12, 35, 0, 45, 0][n])); t=[valuation(n-1, 2), valuation(n-1, 5)]; k=(n-1)\2^t[1]\5^t[2]; if(k>9, return(0)); while(t[1]>t[2]&&2*k<=9, k*=2; t[1]--); while(t[1]<t[2]&&5*k<=9, k*=5; t[2]--); (k*10^vecmax(t)*n)\(n-1) } \\ Max Alekseyev, Apr 13 2009
CROSSREFS
Sequence in context: A055965 A067154 A187486 * A186436 A054670 A277929
KEYWORD
nonn,base
AUTHOR
Lekraj Beedassy, Jul 29 2008
EXTENSIONS
Corrected and extended by Max Alekseyev, Apr 13 2009
STATUS
approved