A031218 Largest prime power <= n.

1, 2, 3, 4, 5, 5, 7, 8, 9, 9, 11, 11, 13, 13, 13, 16, 17, 17, 19, 19, 19, 19, 23, 23, 25, 25, 27, 27, 29, 29, 31, 32, 32, 32, 32, 32, 37, 37, 37, 37, 41, 41, 43, 43, 43, 43, 47, 47, 49, 49, 49, 49, 53, 53, 53, 53, 53, 53, 59, 59, 61, 61, 61, 64, 64, 64, 67, 67, 67, 67, 71, 71

Offset

1,2

Comments

The length of the m-th run of {a(n)} is the length of the (m+1)-st run of A000015 for m > 1. - Colin Linzer, Mar 08 2024

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

B. Dearden, J. Iiams, and J. Metzger, Rumor Arrays, Journal of Integer Sequences, 16 (2013), #13.9.3.

Eric Weisstein's World of Mathematics, Prime Power

Prog

(PARI) a(n)=if(n<1, 0, while(matsize(factor(n))[1]>1, n--); n)
(Haskell)
a031218 n = last $ takeWhile (<= n) a000961_list
-- Reinhard Zumkeller, Apr 25 2011
(Python)
from sympy import factorint
def A031218(n): return next(filter(lambda m:len(factorint(m))<=1, range(n, 0, -1))) # Chai Wah Wu, Oct 25 2024

Crossrefs

Cf. A000015, A000961.

Sequence in context: A345965 A131233 A136623 * A357004 A357005 A267508

Adjacent sequences: A031215 A031216 A031217 * A031219 A031220 A031221

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Erich Friedman

Status

approved