0,3

Maximum number of squares attacked by a bishop on an n X n chessboard - Stewart Gordon (smjg(AT)iname.com), Mar 23 2001

Also number of squares attacked by a bishop on a toroidal chessboard. - Diego Torres (torresvillarroel(AT)hotmail.com), May 30 2001

Numbers n such that {1,2,3,...,n-1,n} is a perfect Skolem set. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 24 2006

The number of terms which lie on the principal diagonals of an n X n square spiral. - William A. Tedeschi (fynmun(AT)hotmail.com), Mar 02 2008

Possible nonnegative discriminants of quadratic equation a*x^2+b*x+c or discrminants of binary quadratic forms a*x^2+b*x*y+c^y^2. - Artur Jasinski (grafix(AT)csl.pl), Apr 28 2008

A133872(a(n)) = 1; complement of A042964. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Oct 03 2008]

T. Skolem, On certain distributions of integers in pairs with given differences, Math. Scand., 1957, vol. 5, 57-68.

G.f.: (x+3*x^2)/((1-x)*(1-x^2)). a(n)=a(n-1)+2+(-1)^n - Michael Somos, Jan 12 2000.

a(n)=-1/2+1/2*(-1)^n+2*n, with n>=0 [From Paolo P. Lava (ppl(AT)spl.at), Oct 03 2008]

a[0]:=0:a[1]:=1:for n from 2 to 100 do a[n]:=a[n-2]+4 od: seq(a[n], n=0..54); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 16 2008

seq(add(irem(3^k, 4), k=4..n), n=3..57); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 20 2008

a:=n->add(2+(-1)^j, j=1..n):seq(a(n), n=0..52); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 13 2008]

bb = {}; Do[Do[Do[d = b^2 - 4 a c; If[d < 0, [null], AppendTo[bb, d]], {a, 0, 50}], {b, 0, 50}], {c, 0, 50}]; Union[bb] - Artur Jasinski (grafix(AT)csl.pl), Apr 28 2008

(PARI) a(n)=2*n-n%2

A042948(n) = A042963(n)-1.

Sequence in context: A154885 A042956 A128217 this_sequence A126001 A073320 A020668

Adjacent sequences: A042945 A042946 A042947 this_sequence A042949 A042950 A042951

nonn

N. J. A. Sloane (njas(AT)research.att.com).