A379313 Positive integers whose prime indices are not all composite.

2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 36, 38, 39, 40, 41, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82

Offset

1,1

Comments

Or, positive integers whose prime indices include at least one 1 or prime number.

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Links

Table of n, a(n) for n=1..67.

Example

The terms together with their prime indices begin:
     2: {1}
     3: {2}
     4: {1,1}
     5: {3}
     6: {1,2}
     8: {1,1,1}
     9: {2,2}
    10: {1,3}
    11: {5}
    12: {1,1,2}
    14: {1,4}
    15: {2,3}
    16: {1,1,1,1}
    17: {7}
    18: {1,2,2}
    20: {1,1,3}
    21: {2,4}
    22: {1,5}
    24: {1,1,1,2}

Mathematica

prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], !And@@CompositeQ/@prix[#]&]

Crossrefs

Partitions of this type are counted by A000041 - A023895.

The "old" primes are listed by A008578.

For no composite parts we have A302540, counted by A034891 (strict A036497).

The complement is A320629, counted by A023895 (strict A204389).

For a unique prime we have A331915, counted by A379304 (strict A379305).

Positions of nonzeros in A379311.

For a unique 1 or prime we have A379312, counted by A379314 (strict A379315).

A000040 lists the prime numbers, differences A001223.

A002808 lists the composite numbers, nonprimes A018252, differences A073783 or A065310.

A055396 gives least prime index, greatest A061395.

A056239 adds up prime indices, row sums of A112798, counted by A001222.

A080339 is the characteristic function for the old prime numbers.

A376682 gives k-th differences of old prime numbers, see A030016, A075526.

A377033 gives k-th differences of composite numbers, see A073445, A377034.

Other counts of prime indices:

- A257991 odd, see A000041, A000070, A066207, A349158.

- A257992 even, see A000009, A038348, A066208, A379317.

- A257994 prime, see A000586, A000607, A076610, A331386.

- A330944 nonprime, see A002095, A096258, A320628, A330945.

- A379306 squarefree, see A302478, A379308, A379309, A379316.

- A379310 nonsquarefree, see A114374, A256012, A379307.

`Cf. A038550, A087436, A173390, A379300, A379301.

Sequence in context: A184520 A047248 A114024 * A030173 A048265 A288712

Adjacent sequences: A379310 A379311 A379312 * A379314 A379315 A379316

Keyword

nonn

Author

Gus Wiseman, Dec 28 2024

Status

approved