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Search: id:A144967
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| A144967 |
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Semiprimes n such that n + 1 is divisible by the sum of decimal digits of n. |
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+0
2
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| 10, 14, 34, 65, 143, 215, 299, 362, 454, 458, 545, 655, 671, 689, 799, 917, 922, 923, 943, 1003, 1007, 1042, 1055, 1111, 1154, 1199, 1253, 1273, 1379, 1507, 1529, 1739, 1807, 1835, 1919, 1957, 2045, 2095, 2183, 2209, 2231, 2279, 2302, 2326, 2342, 2435
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OFFSET
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1,1
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EXAMPLE
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14 and 15 are semiprimes. 14+1 = 15 is divisible by 1+4 = 5, hence 14 is in the sequence; 15+1 = 16 is not divisible by 1+5 = 6, hence 15 is not in the sequence. [From Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Sep 29 2008]
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MATHEMATICA
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Select[Range[5000], Sum[FactorInteger[ # ][[i, 2]], {i, 1, Length[FactorInteger[ # ]]}] == 2 && Mod[ # + 1, Plus @@ IntegerDigits[ # ]] == 0 &] [From Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Sep 29 2008]
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CROSSREFS
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Cf. A001358 (semiprimes). [From Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Sep 29 2008]
Sequence in context: A115391 A164765 A116955 this_sequence A107126 A025122 A167334
Adjacent sequences: A144964 A144965 A144966 this_sequence A144968 A144969 A144970
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KEYWORD
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base,nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Sep 27 2008
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EXTENSIONS
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Corrected and extended by Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) and Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Sep 29 2008
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