A361363 - OEIS

A361363

Primitive terms of A259850.

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

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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).

LINKS

Table of n, a(n) for n=1..50.

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