A201018 Composite numbers whose multiplicative digital root is 5.

15, 35, 51, 57, 75, 115, 135, 153, 175, 315, 351, 355, 395, 511, 513, 517, 531, 535, 539, 553, 575, 579, 597, 715, 755, 759, 795, 935, 957, 975, 1115, 1135, 1157, 1175, 1315, 1351, 1355, 1359, 1395, 1513, 1517, 1535, 1539, 1557, 1575, 1593, 1715, 1751, 1755, 1795

Offset: 1

Author

Jaroslav Krizek, Nov 25 2011

Keywords

• nonn
• base

Comments

Complement of A201017 with respect to A034052.

Examples

			Composite number 153 is in the sequence because 1*5*3=15, 1*5=5.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Multiplicative Digital Root

Crossrefs

Cf. A201017 (primes whose multiplicative digital root is 5), A034052 (numbers whose multiplicative digital root is 5).

Programs

Mathematica

mdr5Q[n_]:=NestWhile[Times@@IntegerDigits[#]&,n,#>9&]==5; Select[Range[1800], CompositeQ[ #] &&mdr5Q[#]&] (* Harvey P. Dale, Dec 19 2023 *)