A364540 Numbers k for which A005940(k) < k.

9, 17, 18, 33, 34, 35, 36, 65, 66, 67, 68, 69, 70, 72, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 140, 144, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 270, 272, 273, 274, 276, 280, 288, 289, 385, 513, 514, 515, 516, 517, 518, 519, 520, 521, 522, 523, 524, 525, 526, 527, 528, 529, 530, 531

Offset: 1

Author

Antti Karttunen, Jul 28 2023

Keywords

• nonn

Crossrefs

Positions of negative terms in A364499.

One more than A356450.

Subsequence of A364541, complement of A364542.

Cf. A005940.

Programs

Mathematica

nn = 540; 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 *)

PARI

A005940(n) = { my(p=2, t=1); n--; until(!n\=2, if((n%2), (t*=p), p=nextprime(p+1))); t };
isA364540(n) = (A005940(n)
				

Formula

a(n) = 1 + A356450(n).