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A260144
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Numbers k such that there exist two numbers a and b where k = a.b = sigma(a)*phi(b) ("." means concatenation).
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2
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OFFSET
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1,1
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COMMENTS
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The sequence is infinite because, for m>0, 14049280*10^m = sigma(1404) * phi(9280*10^m).
a(7) > 10^10.
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LINKS
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Table of n, a(n) for n=1..6.
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EXAMPLE
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1568 is in the sequence because 1568 = sigma(156) * phi(8).
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CROSSREFS
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Cf. A000010, A000203, A159000, A253824.
Sequence in context: A232036 A035765 A107561 * A221105 A236261 A252073
Adjacent sequences: A260141 A260142 A260143 * A260145 A260146 A260147
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KEYWORD
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nonn,base,more
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AUTHOR
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Paolo P. Lava and Giovanni Resta, Jul 17 2015
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STATUS
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approved
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