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Search: id:A162422
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| A162422 |
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Numbers with at least 2 different numbers of digits among their prime factors. |
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+0
2
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| 22, 26, 33, 34, 38, 39, 44, 46, 51, 52, 55, 57, 58, 62, 65, 66, 68, 69, 74, 76, 77, 78, 82, 85, 86, 87, 88, 91, 92, 93, 94, 95, 99, 102, 104, 106, 110, 111, 114, 115, 116, 117, 118, 119, 122, 123, 124, 129, 130, 132, 133, 134, 136, 138, 141, 142, 145, 146, 148, 152
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Complement of A162421. There are no prime numbers in this sequence.
These numbers can also be called factor rough numbers.
Basically, the number of digits of A020639(k) and of A006530(k) must differ
to admit k into the sequence.
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FORMULA
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{k >1: A055642(A020639(k)) <> A055642(A006530(k)) }. - R. J. Mathar, Sep 16 2009
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EXAMPLE
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1111 = 11*101 has factors with different digital lengths. Also it is the first
occurrence that differs from A084891.
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PROGRAM
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(PARI) factorrough(m, n) =
{
local(x, a, j, f, ln);
for(x=m, n, f=0; a = ifactor(x); for(j=2, length(a), ln=length(Str(a[j-1])); if(length(Str(a[j]))!=ln, f=1; break); ); if(f, print1(x", ")); );
}
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CROSSREFS
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Cf. A084891, A162457
Sequence in context: A160078 A066059 A084891 this_sequence A063940 A046442 A101549
Adjacent sequences: A162419 A162420 A162421 this_sequence A162423 A162424 A162425
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KEYWORD
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base,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)hotmail.com), Jul 03 2009
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EXTENSIONS
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Offset set to 1, definition shortened - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 16 2009
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