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

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
      R:= R, k; count:= count+1; S:= S union {s}
   fi fi;
od:
R;

Crossrefs

Cf. A000010, A000203, A259850.

Sequence in context: A305179 A106386 A000232 * A067789 A225400 A180867

Adjacent sequences: A361360 A361361 A361362 * A361364 A361365 A361366

Keyword

nonn

Author

Robert Israel, Mar 09 2023

Status

approved