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A240952
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Smallest number that can be written in exactly n ways as sum of two quarter-squares.
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2
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19, 0, 1, 2, 6, 18, 36, 72, 106, 450, 562, 2312, 1156, 9522, 1381, 8712, 4930, 16562, 13812, 35912, 14862, 233928, 53316, 361250, 40056, 211250, 55981, 1678112, 51106, 1216800, 305256, 610512, 255531
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listen;
history;
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internal format)
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OFFSET
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0,1
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COMMENTS
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LINKS
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EXAMPLE
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a(2) = 1: A245575(1) = #{1+0, 0+1} = 2;
a(3) = 2: A245575(2) = #{2+0, 1+1, 0+2} = 3;
a(4) = 6: A245575(6) = #{6+0, 4+2, 2+4, 0+6} = 4;
a(5) = 18: A245575(18) = #{16+2, 12+6, 9+9, 6+12, 2+16} = 5;
a(6) = 36: A245575(36) = #{36+0, 30+6, 20+16, 16+20, 6+30, 0+36} = 6.
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MATHEMATICA
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nmax = 36000;
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]];
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PROG
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(Haskell)
import Data.List (elemIndex); import Data.Maybe (fromJust)
a240952 = fromJust . (`elemIndex` a245575_list)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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