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Search: id:A118699
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| A118699 |
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Smaller of two consecutive semiprimes with the same digital root. |
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+0
1
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| 146, 226, 278, 346, 1018, 1177, 1273, 1546, 1594, 1865, 1945, 2138, 2545, 2762, 2798, 2869, 3118, 3317, 3817, 4022, 4045, 4069, 4126, 4198, 4213, 4249, 4322, 4417, 4502, 4511, 4918, 5114, 5389, 5438, 5473, 5515, 5645, 5677, 5855, 6169, 6209, 6218, 6362
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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A010888(a(n))=A010888(b(n)) where a(n)=A001358(k), b(n)=A001358(k+1) - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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EXAMPLE
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146 and 155 are two consecutive semiprimes with the same digital root, namely 2.
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PROGRAM
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(PARI) isA001358(n)= { local(f, fct, sumpo); if(n <4, return(0) ); f=factor(n); fct=(matsize(f))[1]; sumpo= sum(i=1, fct, f[i, 2]); if ( sumpo != 2, return(0), return(1) ); } A010888(n)= { if( n %9 != 0, return(n % 9), return(9) ); } { oldr=0; oldn=0; for(n=5, 10000, if( isA001358(n)==1, dr=A010888(n); if(dr==oldr, print1(oldn, ", "); ); oldr=dr; oldn=n; ); ); } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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CROSSREFS
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Cf. A001358.
Sequence in context: A031510 A145915 A119379 this_sequence A043431 A097728 A145212
Adjacent sequences: A118696 A118697 A118698 this_sequence A118700 A118701 A118702
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), May 20 2006
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EXTENSIONS
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Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2006
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