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A061786 Number of distinct sums i^2 + j^2 for 1<=i<=j<=n. 4
1, 3, 6, 10, 15, 21, 27, 34, 42, 52, 61, 72, 83, 94, 108, 122, 135, 151, 165, 183, 200, 218, 234, 254, 275, 296, 317, 339, 361, 387, 409, 434, 460, 484, 512, 542, 570, 598, 627, 661, 689, 722, 753, 784, 821, 854, 888, 925, 960, 998, 1036, 1075, 1109, 1148 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000

EXAMPLE

If the {s+t} sums are generated by addition 2 terms of an S set consisting of n different entries, then at least 1, at most n(n+1)/2=A000217(n) distinct values can be obtained. The set of first n squares gives results falling between these two extremes. E.g. S={1,4,9,16,25,36,49} provides 27 different sums of two, not necessarily different squares: {2,5,8,10,13,17,18,20,25,26,29,32,34,37,40,41,45,50,52,53,58,61,65,72,74,85,98}_ Only a single sum arises more than once: 50=1+49=25+25. Therefore a(7)=(7*8/2)-1=27.

MAPLE

b:= proc(n) b(n):= {seq(n^2+i^2, i=1..n)} end:

s:= proc(n) s(n):= `if`(n=0, {}, b(n) union s(n-1)) end:

a:= n-> nops(s(n)):

seq(a(n), n=1..100);  # Alois P. Heinz, May 07 2014

MATHEMATICA

f[x_] := x^2 Table[Length[Union[Flatten[Table[f[u]+f[w], {w, 1, m}, {u, 1, m}]]]], {m, 1, 75}]

CROSSREFS

Cf. A000217.

Sequence in context: A240443 A033439 A194082 * A171971 A184009 A105334

Adjacent sequences:  A061783 A061784 A061785 * A061787 A061788 A061789

KEYWORD

nonn

AUTHOR

Labos Elemer, Jun 22 2001

STATUS

approved

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Last modified December 8 09:53 EST 2019. Contains 329862 sequences. (Running on oeis4.)