A199978 Nonprime numbers whose multiplicative digital root is 0.
10, 20, 25, 30, 40, 45, 50, 52, 54, 55, 56, 58, 60, 65, 69, 70, 78, 80, 85, 87, 90, 95, 96, 100, 102, 104, 105, 106, 108, 110, 120, 125, 130, 140, 145, 150, 152, 154, 155, 156, 158, 159, 160, 165, 169, 170, 178, 180, 185, 187, 190, 195, 196, 200, 201, 202
Offset: 1
Examples
Number 58 is in sequence because 5*8 = 40, 4*0 = 0.
Crossrefs
Cf. A199977 (primes whose multiplicative digital root is 0).
Programs
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Mathematica
digRoot[n_] := Module[{k = n}, While[k > 9, k = Times @@ IntegerDigits[k]]; k]; Select[Range[300], ! PrimeQ[#] && digRoot[#] == 0 &] (* T. D. Noe, Nov 23 2011 *)
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