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A121383
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a(0)=3. a(n) = number of earlier terms which, each added to n, sum to a square.
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1
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3, 1, 0, 1, 1, 0, 1, 0, 4, 3, 0, 0, 1, 2, 1, 6, 5, 0, 0, 1, 1, 1, 2, 2, 9, 7, 0, 1, 0, 1, 1, 1, 1, 2, 4, 14, 9, 0, 0, 0, 2, 0, 1, 1, 1, 2, 2, 7, 17, 13, 1, 1, 0, 0, 0, 2, 0, 2, 1, 1, 2, 2, 11, 21, 18, 0, 0, 1, 1, 0, 1, 0, 2, 0, 2, 1, 1, 2, 2, 16, 26, 22, 1, 1
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OFFSET
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0,1
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COMMENTS
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Does every nonnegative integer occur eventually? Analogous to A123396 a(0)=0. a(n) = number of earlier terms each of which, when added to n, the sum is a triangular number.
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LINKS
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Giovanni Resta, Table of n, a(n) for n = 0..1000
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EXAMPLE
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a(6) = 1 because the previous terms are 3, 1, 0, 1, 1, 0, and among them only one (3) added to 6 gives a square (9).
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MATHEMATICA
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a[0] = 3; a[n_] := a[n] = Length@ Select[ Range[0, n-1], IntegerQ@ Sqrt[n + a[#]] &]; a /@ Range[0, 90] (* Giovanni Resta, Jun 13 2016 *)
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CROSSREFS
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Cf. A123396.
Sequence in context: A307753 A181116 A051834 * A194521 A181434 A294018
Adjacent sequences: A121380 A121381 A121382 * A121384 A121385 A121386
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post, Oct 14 2006
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EXTENSIONS
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Data section corrected and extended by Giovanni Resta, Jun 13 2016
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STATUS
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approved
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