A071389 Least number m such that cardinality of InvPhi(m) = prime(n).

1, 2, 8, 32, 48, 396, 72, 216, 1056, 1320, 240, 480, 15936, 3072, 7344, 2016, 3024, 9984, 22848, 3360, 13248, 9360, 4800, 9504, 9216, 23328, 7680, 53280, 12480, 29376, 91200, 159744, 22464, 228960, 29952, 179200, 47040, 68544, 15840, 20736, 61440

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Formula

a(n) = Min{x; Card(InvPhi(x)) = prime(n), n-th prime}

Example

For n = 11: prime(11) = 31, Card(InvPhi(x)) = 31 for {240, 672, ...}; the smallest is 240 = a(11).

Prog

(PARI) lista(len) = {my(p = prime(len), v = vector(p, i, -!isprime(i)), c = 0, k = 1, i); while(c < len, i = invphiNum(k); if(i > 0 && i <= p && v[i] == 0, c++; v[i] = k); k++); select(x -> x > 0, v); } \\ Amiram Eldar, Nov 11 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000010, A014197, A058277, A063512, A071386, A071387, A071388.

Sequence in context: A330782 A200063 A238984 * A026369 A269818 A331823

Adjacent sequences: A071386 A071387 A071388 * A071390 A071391 A071392

Keyword

nonn

Author

Labos Elemer, May 23 2002

Extensions

4 more terms from Emeric Deutsch, Jul 25 2005

More terms from Max Alekseyev, Apr 24 2010

Status

approved