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 A162421 Numbers whose prime factors all have the same number of digits. 1
 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; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. LINKS Table of n, a(n) for n=1..70. FORMULA {k >1: A055642(A020639(k)) = A055642(A006530(k)) }. - R. J. Mathar, Sep 16 2009 EXAMPLE 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. PROG (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", ")); ) }; CROSSREFS Cf. A162422 Sequence in context: A274399 A276181 A171829 * A275164 A076499 A092629 Adjacent sequences: A162418 A162419 A162420 * A162422 A162423 A162424 KEYWORD base,nonn AUTHOR Cino Hilliard, Jul 03 2009 EXTENSIONS Offset set to 1 - R. J. Mathar, Sep 16 2009 STATUS approved

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Last modified July 22 22:22 EDT 2024. Contains 374544 sequences. (Running on oeis4.)