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A129476
a(n) is the concatenation in increasing order of all single-digit divisors of n.
1
1, 12, 13, 124, 15, 1236, 17, 1248, 139, 125, 1, 12346, 1, 127, 135, 1248, 1, 12369, 1, 1245, 137, 12, 1, 123468, 15, 12, 139, 1247, 1, 12356, 1, 1248, 13, 12, 157, 123469, 1, 12, 13, 12458, 1, 12367, 1, 124, 1359, 12, 1, 123468, 17, 125
OFFSET
1,2
COMMENTS
Sequence has period 2520 = 2^3 * 3^2 * 5 * 7.
a(n) = 1 iff n is a 11-rough number: not divisible by 2, 3, 5 or 7 (A008364). - Bernard Schott_, Dec 31 2020
LINKS
FORMULA
Let n be the rank and result be the number for this rank let a1...ak be k digits (a1...ak in [0,9]) result=a1*10^(k-1)...ak*10^0 with (i|n) => i in {a1...ak}.
EXAMPLE
a(10)=125 because 1, 2 and 5 divides 10. 10 also divides 10 but it is not a digit so it doesn't appear.
a(2520) = 123456789. - Bernard Schott_, Dec 31 2020
MAPLE
a:= n-> parse(cat(seq(`if`(irem(n, i)=0, i, [][]), i=1..9))):
seq(a(n), n=1..50); # Alois P. Heinz, Dec 31 2020
MATHEMATICA
Table[FromDigits[Select[Divisors[n], #<10&]], {n, 50}] (* Harvey P. Dale, Jun 07 2015 *)
PROG
(PARI) a(n) = fromdigits(select(x->(x<10), divisors(n))); \\ Michel Marcus, Dec 31 2020
(Python)
def a(n): return int('1'+"".join(d for d in "23456789" if n%int(d) == 0))
print([a(n) for n in range(1, 51)]) # Michael S. Branicky, Dec 31 2020
CROSSREFS
Sequence in context: A058950 A064003 A135123 * A243361 A037278 A164852
KEYWORD
nonn,base,easy
AUTHOR
Colin Pitrat (colin.pitrat(AT)rez-gif.supelec.fr), May 29 2007
EXTENSIONS
Editing and comment from Charles R Greathouse IV, Nov 02 2009
More terms from Harvey P. Dale, Jun 07 2015
Name edited by Joerg Arndt, Jan 01 2021
STATUS
approved