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A245585 Numbers that cannot be written as sum of two quarter-squares, cf. A002620. 3
19, 23, 33, 35, 47, 59, 63, 71, 75, 77, 95, 103, 107, 118, 124, 129, 131, 143, 147, 155, 161, 167, 179, 187, 195, 201, 203, 206, 209, 215, 217, 223, 236, 239, 243, 247, 248, 251, 271, 275, 280, 283, 285, 287, 294, 299, 311, 316, 323, 327, 329, 332, 334, 339 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A245575(a(n)) = 0.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

MATHEMATICA

qsQ[n_] := qsQ[n] = With[{s = Sqrt[n]}, Which[IntegerQ[s], True, n == Floor[s] (Floor[s] + 1), True, True, False]];

A245575[n_] := Count[Range[0, n], k_ /; qsQ[k] && qsQ[n - k]];

Flatten[Position[Array[A245575, 1000, 0], 0]] - 1 (* Jean-Fran├žois Alcover, May 08 2017 *)

PROG

(Haskell)

a245585 n = a245585_list !! (n-1)

a245585_list = filter ((== 0) . a245575) [0..]

CROSSREFS

Cf. A002620, A245575.

Sequence in context: A261311 A168144 A108271 * A060269 A245382 A075585

Adjacent sequences:  A245582 A245583 A245584 * A245586 A245587 A245588

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Aug 04 2014

STATUS

approved

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Last modified February 22 10:53 EST 2020. Contains 332135 sequences. (Running on oeis4.)