OFFSET
1,1
COMMENTS
The numbers not of the form x^2+2y^2+5z^2.
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
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) ~ 12 * n. - David A. Corneth, Apr 12 2015
EXAMPLE
a(19) = a(1) + 25 * floor((19 - 1)/2) = 235 - David A. Corneth, Mar 31 2015
MAPLE
N:= 1000: # to get all terms <= N
A:= {}:
for i from 0 to floor((log[5](N)-1)/2) do
a:= 5^(2*i+1);
A:= A union {seq(a*(5*j+2), j=0..floor((N/a-2)/5))}
union {seq(a*(5*j-2), j=1..floor((N/a+2)/5))};
od:
A; # if using Maple 11 or earlier, uncomment the next line
# sort(convert(A, list)); # Robert Israel, Apr 13 2015
MATHEMATICA
Take[ Union@ Flatten@ Table[ 5^(2i + 1) (j), {i, 0, 1}, {j, Select[ Range@ 120, Mod[#, 5] == 2 || Mod[#, 5] == 3 &] }], 50] (* Robert G. Wilson v, Mar 30 2015 *)
PROG
(PARI) is(n) = v=valuation(n, 5); r=(n/5^v)%5; v%2==1&&(r==2||r==3) \\ David A. Corneth, Apr 12 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 02 2000
STATUS
approved