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A361363
Primitive terms of A259850.
1
1, 3, 8, 14, 15, 21, 26, 40, 130, 144, 182, 255, 310, 372, 465, 468, 680, 980, 1524, 2170, 2210, 2418, 2448, 4030, 4536, 7008, 7956, 8890, 9906, 10220, 10416, 10668, 12648, 16335, 16660, 17082, 20216, 24624, 30800, 36792, 41106, 44055, 48400, 65535, 77112, 78320, 85120, 97790, 143000, 149688
OFFSET
1,2
COMMENTS
Terms k of A259850 such that no earlier term of A259850 has the same set of prime factors as k.
Numbers k such that k/phi(k) = sigma(x)/x for some x<=k, and there do not exist m and y with y <= m < k such that m has the same set of prime factors as k and sigma(y)/y = k/phi(k).
EXAMPLE
a(4) = 14 is a term because 14 = A259850(5) is the first term of A259850 whose set of prime factors is {2,7}.
28 = A259850(11) is not a term because it has the same set {2,7} of prime factors as 14.
MAPLE
R:= NULL: count:= 0: V:= {}: S:= {}:
for k from 1 while count < 50 do
V:= V union {numtheory:-sigma(k)/k};
if member(k/numtheory:-phi(k), V) then
s:= numtheory:-factorset(k);
if not member(s, S) then
R:= R, k; count:= count+1; S:= S union {s}
fi fi;
od:
R;
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Mar 09 2023
STATUS
approved