OFFSET
1,1
COMMENTS
Numbers not of the form x^2+2y^2+6z^2.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
L. E. Dickson, Integers represented by positive ternary quadratic forms, Bull. Amer. Math. Soc. 33 (1927), 63-70. See Theorem XI.
L. J. Mordell, A new Waring's problem with squares of linear forms, Quart. J. Math., 1 (1930), 276-288 (see p. 283).
FORMULA
a(n) = 6n + O(log n). - Charles R Greathouse IV, Dec 19 2013
PROG
(PARI) is(n)=n/=4^valuation(n, 4); n%8==5 \\ Charles R Greathouse IV and V. Raman, Dec 19 2013
(Haskell)
a055045 n = a055045_list !! (n-1)
a055045_list = filter ((== 5) . (flip mod 8) . f) [1..] where
f x = if r == 0 then f x' else x where (x', r) = divMod x 4
-- Reinhard Zumkeller, Jan 02 2014
(Python)
from itertools import count, islice
def A055045_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n:not (m:=(~n&n-1).bit_length())&1 and (n>>m)&7==5, count(max(startvalue, 1)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jun 01 2000
STATUS
approved