A359397 - OEIS

A359397

Squarefree numbers with weakly decreasing first differences of 0-prepended prime indices.

1, 2, 3, 5, 6, 7, 11, 13, 15, 17, 19, 21, 23, 29, 30, 31, 35, 37, 41, 43, 47, 53, 55, 59, 61, 65, 67, 71, 73, 77, 79, 83, 89, 91, 97, 101, 103, 105, 107, 109, 113, 119, 127, 131, 133, 137, 139, 143, 149, 151, 157, 163, 167, 173, 179, 181, 187, 191, 193, 197

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OFFSET

1,2

COMMENTS

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..60.

FORMULA

Intersection of A325362 and A005117.

EXAMPLE

715 has prime indices {3,5,6}, with first differences (2,1), which are weakly decreasing, so 715 is in the sequence.

MATHEMATICA

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

Select[Range[100], SquareFreeQ[#]&&GreaterEqual@@Differences[Prepend[primeMS[#], 0]]&]

CROSSREFS

This is the squarefree case of A325362.

These are the sorted Heinz numbers of rows of A359361.

A005117 lists squarefree numbers.

A112798 lists prime indices, length A001222, sum A056239, reverse A296150.

A355536 lists first differences of prime indices, 0-prepended A287352.

A358136 lists partial sums of prime indices, row sums A318283.

Cf. A000009, A000720, A001221, A253566, A261079, A304818, A358137, A358169.

Sequence in context: A308420 A363462 A260442 * A098962 A073485 A377201

Adjacent sequences: A359394 A359395 A359396 * A359398 A359399 A359400

KEYWORD

nonn

AUTHOR

Gus Wiseman, Dec 31 2022

STATUS

approved