A060845 Largest prime < a nontrivial power of a prime.

3, 7, 7, 13, 23, 23, 31, 47, 61, 79, 113, 113, 127, 167, 241, 251, 283, 337, 359, 509, 523, 619, 727, 839, 953, 1021, 1327, 1367, 1669, 1847, 2039, 2179, 2179, 2207, 2399, 2803, 3121, 3469, 3719, 4093, 4483, 4909, 5039, 5323, 6229, 6553, 6857, 6883, 7919

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Formula

a(n) = prevprime[A025475(n)] = A007917[A025475(n)] = Max{p| p < A025475(n)}

Example

78125=5^7 follows 78121

Mathematica

Take[NextPrime[#, -1]&/@Union[Flatten[Table[Prime[p]^n, {n, 2, 20}, {p, 25}]]], 50] (* Harvey P. Dale, Mar 26 2012 *)

Prog

(PARI) { m=1; for (n=1, 1000, m++; while(sigma(m)*eulerphi(m)*(1 - isprime(m)) <= (m - 1)^2, m++); write("b060845.txt", n, " ", precprime(m - 1)); ) } \\ Harry J. Smith, Jul 19 2009

Crossrefs

Cf. A025475, A000961, A001597, A001694, A007917, A007918, A013632, A013633, A049711, A060846.

Sequence in context: A064829 A290649 A118259 * A059478 A175329 A081218

Adjacent sequences: A060842 A060843 A060844 * A060846 A060847 A060848

Keyword

nonn

Author

Labos Elemer, May 03 2001

Status

approved