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