OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Multiplicative Digital Root
EXAMPLE
Composite number 153 is in the sequence because 1*5*3=15, 1*5=5.
MATHEMATICA
mdr5Q[n_]:=NestWhile[Times@@IntegerDigits[#]&, n, #>9&]==5; Select[Range[1800], CompositeQ[ #] &&mdr5Q[#]&] (* Harvey P. Dale, Dec 19 2023 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 25 2011
STATUS
approved