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A071011 Numbers n such that n is a sum of 2 squares (i.e., n is in A001481(k)) and sigma(n) == 0 (mod 4). 1
65, 85, 125, 130, 145, 170, 185, 205, 221, 250, 260, 265, 290, 305, 340, 365, 370, 377, 410, 442, 445, 481, 485, 493, 500, 505, 520, 530, 533, 545, 565, 580, 585, 610, 629, 680, 685, 689, 697, 730, 740, 745, 754, 765, 785, 793, 820, 865, 884, 890, 901, 905 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

It is conjectured that if m is not a sum of 2 squares (i.e., m is in A022544(k)) sigma(m) == 0 (mod 4).

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[10^3], And[SquaresR[2, #] > 0, Divisible[DivisorSigma[1, #], 4]] &] (* Michael De Vlieger, Jul 30 2017 *)

PROG

(PARI) for(n=1, 1000, if(1-sign(sum(i=0, n, sum(j=0, i, if(i^2+j^2-n, 0, 1))))+sigma(n)%4==0, print1(n, ", ")))

CROSSREFS

Cf. A001481, A022544.

Sequence in context: A025312 A024508 A025303 * A165158 A084648 A224770

Adjacent sequences:  A071008 A071009 A071010 * A071012 A071013 A071014

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, May 19 2002

STATUS

approved

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Last modified January 26 11:45 EST 2022. Contains 350598 sequences. (Running on oeis4.)