OFFSET
1,1
COMMENTS
Smallest pandigital n-almost prime.
FORMULA
EXAMPLE
a(1) = 10123457689 is the least prime pandigital number (A221646), that is, the smallest prime containing all the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
a(2) = 10123456789 = 919 * 11015731, the smallest pandigital semiprime.
a(3) = 1023456879, the smallest pandigital number (A171102) that is 3-almost prime (product of three primes with repetition).
a(4) = 1023456987 = 3^2 * 7 * 16245349, which is the smallest pandigital 4-almost prime.
a(5) = 1023456897 = 3^3 * 2417 * 15683.
a(6) = 1023456789 = 3^4 * 2221 * 5689.
a(7) = 1023456798 = 2 * 3^2 * 7 * 13 * 487 * 1283.
a(8) = 1023457896 = 2^3 * 3^3 * 59 * 80309.
MATHEMATICA
a[n_] := Block[{k = If[n < 3, 10123456789, 1023456789]}, While[ Union@ IntegerDigits@ k != Range[0, 9] || Total[Last /@ FactorInteger[k]] != n, k++]; k]; Array[a, 10] (* Giovanni Resta, May 06 2013 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, May 04 2013
EXTENSIONS
a(2) corrected and a(9)-a(21) from Giovanni Resta, May 06 2013
STATUS
approved