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Search: id:A147624
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| A147624 |
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Numbers n = concat(a,b) such that omega(n) = omega(a) * omega(b), where omega = A001221. |
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+0
4
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| 23, 25, 26, 27, 29, 32, 36, 37, 43, 46, 47, 49, 53, 56, 59, 62, 63, 65, 68, 69, 73, 76, 79, 83, 86, 89, 96, 97, 104, 108, 113, 116, 122, 123, 124, 129, 136, 137, 139, 142, 143, 144, 145, 147, 148, 152, 153, 155, 158, 159, 163, 166, 167, 169, 173, 176, 179, 183, 184
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Concat(a,b) means decimal concatenation of a and b, i.e. a*10^[log[10](b)+1] + b, since we don't allow leading zeros in b.
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EXAMPLE
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a(1)=23 is in the sequence since omega(23) = 1 = 1*1 = omega(2)*omega(3).
307 is not in this sequence although omega(307) = 1 = 1*1 = omega(3)*omega(07), since we don't allow leading zeros in the second part b.
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PROGRAM
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(PARI) is_A147624(n)={ local(p=1, o=omega(n)); while( n>p*=10, n%p*10<p & next; o == omega( n\p )*omega( n%p ) & return(1))}
for( n=1, 999, is_A147624(n) & print1(n", "))
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CROSSREFS
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Cf. A001221, A147616 (analogue for sigma), A147619 (analogue for eulerphi), A147627 (analogue for bigomega).
Sequence in context: A042101 A042102 A156964 this_sequence A095251 A054865 A054795
Adjacent sequences: A147621 A147622 A147623 this_sequence A147625 A147626 A147627
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KEYWORD
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base,easy,nonn
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AUTHOR
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M. F. Hasler (MHasler(AT)univ-ag.fr), Nov 08 2008
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