A199983 -id:A199983 - cp's OEIS frontend

A199984 Composite numbers whose multiplicative digital root is 4.

4, 14, 22, 27, 39, 72, 93, 98, 114, 122, 141, 172, 189, 198, 212, 217, 221, 249, 266, 294, 319, 333, 338, 346, 364, 391, 411, 429, 436, 492, 626, 634, 662, 712, 721, 767, 772, 776, 793, 819, 833, 891, 913, 918, 924, 931, 942, 973, 981, 1114, 1122, 1127, 1139

Offset: 1

Jaroslav Krizek, Nov 13 2011

Complement of A199983 with respect to A034051.

			Number 172 is in sequence because 1*7*2=14, 1*4=4.

Cf. A199983 (primes whose multiplicative digital root is 4).

Cf. A034051 (numbers whose multiplicative digital root is 4).

cn4Q[n_]:=NestWhile[Times@@IntegerDigits[#]&,n,#>9&]==4; Select[Select[ Range[ 1200],CompositeQ],cn4Q] (* Harvey P. Dale, Apr 28 2018 *)

A201016 Composite numbers whose product of digits is 4.

Original entry on oeis.org

4, 14, 22, 114, 122, 141, 212, 221, 411, 1114, 1122, 1141, 1212, 1221, 1411, 2112, 2121, 2211, 11114, 11122, 11141, 11212, 11221, 12112, 12121, 14111, 21112, 41111, 111114, 111122, 111141, 111212, 111221, 111411, 112112, 112211, 114111, 121112, 121121, 121211, 122111

Offset: 1

Jaroslav Krizek, Nov 25 2011

Complement of A107690 with respect to A199987. Subsequence of A199983 (composite numbers whose multiplicative digital root is 4).

			Number 122 is in sequence because 1*2*2=4.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A107690 (primes whose product of digits is 4), A199987 (numbers whose product of digits is 4).

Select[Range[125000],CompositeQ[#]&&Times@@IntegerDigits[#]==4&] (* or *) Module[{nn=6,f,t},f=Flatten[Table[Select[FromDigits/@Permutations[PadRight[{4},d,1]],CompositeQ],{d,nn}]];t=Flatten[Table[Select[FromDigits/@Permutations[PadRight[{2,2},d,1]],CompositeQ],{d,nn}]];Join[f,t]]//Sort (* The second program is much faster than the first. *) (* Harvey P. Dale, May 15 2025 *)

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A199984 Composite numbers whose multiplicative digital root is 4.

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