OFFSET
1,1
COMMENTS
[k/2]+[k/4]+[k/8]+[k/16]+... = prevprime(k).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1001 terms from Harvey P. Dale)
EXAMPLE
8! = 2^7*3^2*5*7, 23! = 2^19*3^9*5^4*7^3*11^2*13*17*19*23.
MAPLE
for n from 3 to 10^3 do if sum(floor(n/(2^i)), i=1..15) = prevprime(n) then printf(`%d, `, n) fi; od:
# second Maple program:
b:= proc(n) option remember;
`if`(n<1, 0, b(n-1)+padic[ordp](n, 2))
end:
a:= proc(n) option remember; local k; for k from 1+
`if`(n=1, 2, a(n-1)) while b(k)<>prevprime(k) do od; k
end:
seq(a(n), n=1..100); # Alois P. Heinz, Jul 10 2022
MATHEMATICA
Select[Range[400], IntegerExponent[#!, 2]==NextPrime[#, -1]&] (* Harvey P. Dale, Sep 24 2013 *)
PROG
(Python 3.10+)
from itertools import count, islice
from sympy import prevprime
def A064394_gen(startvalue=3): # generator of terms
return filter(lambda n:n-n.bit_count()==prevprime(n), count(max(startvalue, 3)))
(PARI) isok(k) = (k>1) && (valuation(k!, 2) == precprime(k-1)); \\ Michel Marcus, Jul 10 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Sep 29 2001
EXTENSIONS
More terms from James A. Sellers, Oct 01 2001
Name clarified and offset changed to 1 by Chai Wah Wu, Jul 10 2022
STATUS
approved