A364541 Numbers k for which A005940(k) <= k.

1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 16, 17, 18, 20, 24, 32, 33, 34, 35, 36, 40, 48, 64, 65, 66, 67, 68, 69, 70, 72, 80, 96, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 140, 144, 160, 192, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 270, 272, 273, 274, 276, 280, 288, 289, 320, 384, 385, 512

Offset

1,2

Comments

A029747 is included as a subsequence, because it gives the known fixed points of map n -> A005940(n).

Links

Table of n, a(n) for n=1..72.

Mathematica

nn = 512; Array[Set[a[#], #] &, 2]; Do[If[EvenQ[n], Set[a[n], 2 a[n/2]], Set[a[n], Times @@ Power @@@ Map[{Prime[PrimePi[#1] + 1], #2} & @@ # &, FactorInteger[a[(n + 1)/2]]]]], {n, 3, nn}]; Select[Range[nn], a[#] <= # &] (* Michael De Vlieger, Jul 28 2023 *)

Prog

(PARI)
A005940(n) = { my(p=2, t=1); n--; until(!n\=2, if((n%2), (t*=p), p=nextprime(p+1))); t };
isA364541(n) = (A005940(n)<=n);

Crossrefs

Positions of nonpositive terms in A364499.

Cf. A005940, A364542.

Subsequences: A029747, A364540.

Sequence in context: A018412 A061945 A029509 * A048645 A173786 A093863

Adjacent sequences: A364538 A364539 A364540 * A364542 A364543 A364544

Keyword

nonn

Author

Antti Karttunen, Jul 28 2023

Status

approved