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A226186
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Composite numbers with both additive and multiplicative digital roots prime.
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2
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12, 21, 34, 57, 75, 115, 232, 299, 322, 371, 376, 398, 511, 579, 597, 637, 713, 731, 736, 759, 763, 795, 893, 938, 957, 975, 992, 1112, 1121, 1137, 1157, 1173, 1175, 1211, 1299, 1317, 1355, 1371, 1389, 1398, 1469, 1474, 1496, 1517, 1535, 1649, 1694
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OFFSET
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1,1
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LINKS
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EXAMPLE
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322 is here since for 322 additive digital root is 7 and multiplicative digital root is 2, both are primes.
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MATHEMATICA
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a[n_] := NestWhile[Times@@IntegerDigits[#]&, n, #>9&]; Select[Range[1700], !PrimeQ[#] && And@@PrimeQ[{a[#], Mod[#, 9]}]&]
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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