OFFSET
1,2
COMMENTS
If NA(1)A(2)...A(j)N is MDR strong then also Na(1)a(2)...a(j)N is MDR strong where a(1)a(2)...a(j) is any permutation of A(1)A(2)...A(j) and if any of A(1),A(2),...,A(j) say A(1) is composite then also NB(1)...B(k)A(2)...A(j) is MDR strong where A(1)=B(1)*B(2)*...*B(k), so MDR strong numbers with greater number of digits are likely to be more frequent.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MATHEMATICA
dr[n_]:=NestWhile[Times@@IntegerDigits[#]&, n, #>9&]; bemdrQ[n_]:=Module[ {idn=IntegerDigits[n]}, First[idn]==Last[idn]==dr[n]]; Select[Range[ 12000], bemdrQ] (* Harvey P. Dale, Oct 21 2011 *)
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Santi Spadaro, Oct 13 2001
STATUS
approved