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A273318 Numbers n such that n+k-1 is the sum of two nonzero squares in exactly k ways for all k = 1, 2, 3. 3
58472, 79208, 104616, 150048, 160848, 205648, 224648, 234448, 252808, 259648, 259920, 294048, 297448, 387648, 421648, 433448, 462976, 488448, 506248, 563048, 621448, 683648, 770976, 790848, 799648, 837448, 1008648, 1040848, 1084904, 1186632, 1195648, 1205648, 1212064 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that n+k-1 is the sum of two nonzero squares in exactly 4-k ways for all k = 1, 2, 3 are 22984, 65600, 80800, 85544, ...

LINKS

Robert Israel, Table of n, a(n) for n = 1..1095

EXAMPLE

58472 is a term because;

58472 = 86^2 + 226^2.

58473 = 48^2 + 237^2 = 147^2 + 192^2.

58474 = 57^2 + 235^2 = 125^2 + 207^2 = 143^2 + 195^2.

MAPLE

N:= 10^6: # get all terms <= N-2

R:= Vector(N):

for x from 1 to floor(sqrt(N)) do

  for y from 1 to min(x, floor(sqrt(N-x^2))) do

    R[x^2+y^2]:= R[x^2+y^2]+1

od od:

count:= 0:

for n from 1 to N-2 do

  if [R[n], R[n+1], R[n+2]] = [1, 2, 3] then

  count:= count+1; A[count]:= n;

fi

od:

seq(A[i], i=1..count); # Robert Israel, May 19 2016

PROG

(PARI) is(n, k) = {nb = 0; lim = sqrtint(n); for (x=1, lim, if ((n-x^2 >= x^2) && issquare(n-x^2), nb++); ); nb == k; }

isok(n) = is(n, 1) && is(n+1, 2) && is(n+2, 3);

CROSSREFS

Cf. A000404, A025284, A025285, A025286.

Sequence in context: A227496 A295448 A220987 * A230576 A075980 A031684

Adjacent sequences:  A273315 A273316 A273317 * A273319 A273320 A273321

KEYWORD

nonn

AUTHOR

Altug Alkan, May 19 2016

STATUS

approved

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Last modified May 12 04:19 EDT 2021. Contains 343810 sequences. (Running on oeis4.)