A364545 - OEIS

%I #6 Jul 28 2023 16:03:16

%S 1,3,5,125,245,375,715,845,847,1215,2873,11583,12635,21879,24255,

%T 31213,33495,36125,42875,48125,48841,71269,100793,102245,104907,

%U 157035,173641,191607,206045,240787,244205,251459,302575,313937,351509,359513,375687,384475,388531,417605,419957,444889,468999,521703,586177,635375

%N Odd numbers k such that k divides A005940(k).

%t nn = 2^20; 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[1, nn, 2], Divisible[a[#], #] &] (* _Michael De Vlieger_, Jul 28 2023 *)

%o (PARI)

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

%o isA364545(n) = ((n%2)&&!(A005940(n)%n));

%Y Odd terms in A364544.

%Y Cf. A005940, A364501.

%Y Cf. also A364495, A364547.

%K nonn

%O 1,2

%A _Antti Karttunen_, Jul 28 2023