1,1

Area of a Maltese cross conventionally inscribed in a 5n X 5n-grid.

a(n) = A002522(4*n) = A016802(n) + 1.

Areas of some other crosses, each made from unit squares, as shown in Weisstein's illustrations: Greek Cross = x-pentomino = 5. Latin Cross = 6. Saint Andrew's cross = crux decussata = 9. Saint Anthony's Cross = tau cross = crux commissa = 10. Gaullist Cross = cross of lorraine or patriarchal cross = 13. Papal Cross = 22. - Jonathan Vos Post (jvospost3(AT)gmail.com), Jun 18 2005

If A=[A158488] 64*n.^2+8 (n>0, 72, 264, 584,.,); Y=[A005843] 2*n (n>0, 2, 4, 6,.,); X = [A108211] 16*n^2-1 (n>0, 17, 65, 145, .,), we have, for all terms, Pell's equation X^2-A*Y^2=1. Example: 17^2-72*2^2=1; 65^2-264*4^2=1; 145^2-584*6^2=1. [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 20 2009]

Eric Weisstein's World of Mathematics, Maltese Cross

Eric Weisstein's World of Mathematics, Gaullist Cross.

Eric Weisstein's World of Mathematics, Greek Cross.

Eric Weisstein's World of Mathematics, Latin Cross.

Edward Everett Withford, Pell Equation [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 20 2009]

Vincenzo Librandi, X^2-AY^2=1 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 20 2009]

Wolfram MathWorld, Pell Equation [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 20 2009]

Cf. A005843, A158488 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Mar 20 2009]

Sequence in context: A125992 A054402 A086533 this_sequence A130885 A036545 A146807

Adjacent sequences: A108208 A108209 A108210 this_sequence A108212 A108213 A108214

nonn

Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jun 15 2005