A073721 Numbers k such that PrimePi(k) divides sigma(k).
2, 3, 5, 6, 7, 14, 15, 21, 29, 38, 44, 57, 66, 78, 92, 94, 95, 106, 108, 114, 116, 118, 120, 133, 154, 174, 177, 182, 188, 232, 255, 300, 304, 305, 349, 351, 359, 413, 417, 418, 468, 488, 506, 526, 595, 615, 629, 688, 872, 945, 954, 1001, 1002, 1006, 1011, 1018
Offset: 1
Keywords
Links
- Amiram Eldar, Table of n, a(n) for n = 1..1600
Programs
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Mathematica
Do[s=Mod[DivisorSigma[1, n], PrimePi[n]]; If[s==0, Print[n]], {n, 1, 2500}] Select[Range[2,1200],Divisible[DivisorSigma[1,#],PrimePi[#]]&] (* Harvey P. Dale, Jan 31 2014 *) -
PARI
isok(k) = k > 1 && !(sigma(k) % primepi(k)); \\ Amiram Eldar, Mar 18 2025
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PARI
list(lim) = {my(prv = 2, i = 0); forprime(p = 3, lim, i++; for(k = prv, p-1, if(!(sigma(k) % i), print1(k, ", "))); prv = p);} \\ Amiram Eldar, Mar 18 2025