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 A260144 Numbers k such that there exist two numbers a and b where k = a.b = sigma(a)*phi(b) ("." means concatenation). 2
 1568, 14049280, 140492800, 368089904, 506300928, 1404928000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The sequence is infinite because, for m>0, 14049280*10^m = sigma(1404) * phi(9280*10^m). a(7) > 10^10. LINKS EXAMPLE 1568 is in the sequence because 1568 = sigma(156) * phi(8). CROSSREFS Cf. A000010, A000203, A159000, A253824. Sequence in context: A232036 A035765 A107561 * A221105 A236261 A252073 Adjacent sequences: A260141 A260142 A260143 * A260145 A260146 A260147 KEYWORD nonn,base,more AUTHOR Paolo P. Lava and Giovanni Resta, Jul 17 2015 STATUS approved

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Last modified March 27 02:29 EDT 2023. Contains 361553 sequences. (Running on oeis4.)