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Search: id:A162421
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| A162421 |
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Numbers whose prime factors all have the same number of digits. |
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+0
2
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| 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 27, 28, 29, 30, 31, 32, 35, 36, 37, 40, 41, 42, 43, 45, 47, 48, 49, 50, 53, 54, 56, 59, 60, 61, 63, 64, 67, 70, 71, 72, 73, 75, 79, 80, 81, 83, 84, 89, 90, 96, 97, 98, 100, 101, 103, 105, 107
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The prime numbers A000040 are a subset of this sequence.
A number k>1 is in this sequence, if the count of base-10 digits of
all entries in the k-th row of A027746 (=its prime factors) is the same.
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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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16 = 2*2*2*2 and the digital length = 1 for all factors. So 16 is in the
sequence. 22=2*11 is not in the sequence because the digital length of 11 is
not the same as the digital length of 2.
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PROGRAM
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(PARI) factorsmooth(n) =
{
local(x, a, j, f, ln);
for(x=2, n, f=0; a = ifactor(x); ln=length(Str(a[1])); for(j=2, length(a), if(length(Str(a[j]))!=ln, f=1; break); ); if(!f, print1(x", ")); )
};
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CROSSREFS
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Cf. A162422
Sequence in context: A032517 A062996 A085380 this_sequence A076499 A092629 A108192
Adjacent sequences: A162418 A162419 A162420 this_sequence A162422 A162423 A162424
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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 - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 16 2009
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