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A255771
Number of distinct prime factors of A220294(n).
4
1, 1, 1, 2, 2, 1, 2, 2, 4, 2, 2
OFFSET
0,4
COMMENTS
These are the first differences of A255770.
REFERENCES
Arthur Engel, Problem-Solving Strategies, Springer, 1998, pages 121-122 (E3, said to be a "recent competition problem from the former USSR").
EXAMPLE
A220294(0) = 3 so a(0) = 1.
A220294(1) = 13 so a(1) = 1.
A220294(2) = 241 so a(2) = 1.
A220294(3) = 97*673 so a(3) = 2.
A220294(4) = 193*22253377 so a(4) = 2.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Hans Havermann, Mar 06 2015
EXTENSIONS
Offset changed by Arkadiusz Wesolowski, Aug 01 2016
a(9) was found in 2008 by Geoffrey Reynolds. a(10) was found by Anders Björn and Hans Riesel. - Arkadiusz Wesolowski, Aug 02 2016
STATUS
approved