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A198775 Numbers having exactly four representations by the quadratic form x^2+xy+y^2 with 0<=x<=y. 8
1729, 2821, 3367, 3913, 4123, 4459, 4921, 5187, 5551, 5719, 6097, 6517, 6643, 6916, 7189, 7657, 8029, 8113, 8463, 8827, 8911, 9139, 9331, 9373, 9709, 9919, 10101, 10507, 10621, 10633, 11137, 11284, 11557, 11739, 12369, 12649, 12691, 12901, 13237, 13377 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A088534(a(n)) = 4; subsequence of A118886, see also A003136.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..250

EXAMPLE

a(1) = 1729 = 3^2+3*40+40^2 = 8^2+8*37+37^2 = 15^2+15*32+32^2 = 23^2+23*25+25^2, A088534(1729) = 4;

a(10) = 5719 = 5^2+5*73+73^2 = 15^2+15*67+67^2 = 18^2+18*65+65^2 = 37^2+37*50+50^2, A088534(5719) = 4;

a(100) = 23779 = 17^2+17*145+145^2 = 30^2+30*137+137^2 = 50^2+50*123+123^2 = 85^2+85*93+93^2, A088534(23779) = 4.

PROG

(Haskell)

a198775 n = a198775_list !! (n-1)

a198775_list = filter ((== 4) . a088534) a003136_list

CROSSREFS

Cf. A198772, A198773, A198774.

Sequence in context: A154717 A051388 A033181 * A154729 A083737 A182208

Adjacent sequences:  A198772 A198773 A198774 * A198776 A198777 A198778

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 30 2011

STATUS

approved

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Last modified June 25 19:53 EDT 2017. Contains 288729 sequences.