A085347 Least number x so that number of primes not exceeding sigma(x) equals n.

0, 2, 5, 4, 6, 8, 10, 19, 12, 29, 16, 18, 20, 43, 33, 28, 24, 32, 67, 30, 45, 57, 44, 36, 52, 101, 63, 85, 91, 48, 64, 86, 137, 66, 149, 99, 106, 163, 60, 129, 88, 80, 105, 72, 197, 104, 100, 84, 147, 229, 90, 114, 112, 96, 171, 148, 136, 201, 108, 281, 138, 152, 172

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..500

Formula

a(n) = Min{x; A070803(x)=n};

Mathematica

{0}~Join~Table[x = 1; While[PrimePi@ DivisorSigma[1, x] != n, x++]; x, {n, 2, 63}] (* Michael De Vlieger, Feb 05 2017 *)

Prog

(PARI) a(n) = if (n==1, 0, x = 1; while(primepi(sigma(x))!= n,  x++); x); \\ Michel Marcus, Dec 11 2013

Crossrefs

Cf. A000720, A000010, A000203, A070803, A070804, A085341-A085347.

Sequence in context: A132698 A358181 A114557 * A066337 A129491 A021801

Adjacent sequences: A085344 A085345 A085346 * A085348 A085349 A085350

Keyword

nonn

Author

Labos Elemer, Jul 10 2003

Status

approved