A341593 - OEIS

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A341593

Number of superior prime-power divisors of n.

25

0, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 0, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 0, 1, 1, 1, 4, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 0, 1, 1, 1

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OFFSET

1,4

COMMENTS

We define a divisor d|n to be superior if d >= n/d. Superior divisors are counted by A038548 and listed by A161908.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

The superior prime-power divisors (columns) of selected n:

n = 4374 5103 6144 7500 9000

----------------------------

81 81 128 125 125

243 243 256 625

729 729 512

2187 1024

2048

MATHEMATICA

Table[Length[Select[Divisors[n], PrimePowerQ[#]&&#>=n/#&]], {n, 100}]

PROG

(PARI) a(n) = sumdiv(n, d, d^2 >= n && isprimepower(d)); \\ Amiram Eldar, Nov 01 2024

CROSSREFS

Positions of zeros after the first are A051283.

The inferior version is A333750.

The version for prime instead of prime-power divisors is A341591.

The version for squarefree instead of prime-power divisors is A341592.

Dominates A341644 (the strictly superior case).

The version for odd instead of prime-power divisors is A341675.

The strictly inferior version is A341677.

A000961 lists prime powers.

A001221 counts prime divisors, with sum A001414.

A001222 counts prime-power divisors.

A005117 lists squarefree numbers.

A033677 selects the smallest superior divisor.

A038548 counts superior (or inferior) divisors.

A056924 counts strictly superior (or strictly inferior) divisors.

A161908 lists superior divisors.

A207375 lists central divisors.

- Inferior: A033676, A063962, A066839, A069288, A161906, A217581, A333749.

- Superior: A059172, A063538, A063539, A070038, A116882, A116883, A341676.

- Strictly Inferior: A060775, A070039, A333805, A333806, A341596, A341674.

- Strictly Superior: A048098, A064052 A140271, A238535, A341594, A341595, A341642, A341643, A341645, A341646, A341673.

Cf. A000005, A000203, A001248, A006530, A020639, A112798.

Sequence in context: A086074 A180601 A331048 * A288636 A089723 A363741

Adjacent sequences: A341590 A341591 A341592 * A341594 A341595 A341596

KEYWORD

nonn

AUTHOR

Gus Wiseman, Feb 19 2021

STATUS

approved