login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A071010 Sigma(k)/4 when k is not a sum of 2 squares. 1
1, 3, 2, 3, 7, 6, 6, 5, 8, 9, 6, 15, 10, 14, 18, 8, 12, 12, 15, 14, 24, 11, 21, 18, 12, 31, 18, 30, 18, 30, 20, 15, 42, 24, 26, 36, 17, 24, 36, 18, 31, 35, 24, 42, 20, 21, 56, 33, 30, 45, 28, 42, 32, 36, 30, 63, 39, 54, 26, 48, 27, 70, 54, 38, 62, 60, 36, 45, 36, 90, 42, 56, 78 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjecture : if n is not the sum of 2 squares sigma(n) == 0 (mod 4) (converse is not true : if sigma(n) == 0 (mod 4), n is sometimes the sum of 2 squares : sigma(65) = 84 == 0 (mod 4) but 65 = 49+16 is a sum of 2 squares).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = sigma(A022544(n))/4.

MATHEMATICA

DivisorSigma[1, Select[Range[120], SquaresR[2, #] == 0 &]]/4  (* Amiram Eldar, May 13 2022 *)

PROG

(PARI) for(n=0, 200, if(sum(i=0, n, sum(j=0, i, if(i^2+j^2-n, 0, 1)))==0, print1(sigma(n)/4, ", ")))

CROSSREFS

Cf. A000203, A022544.

Sequence in context: A332057 A275330 A141863 * A343231 A215934 A323895

Adjacent sequences:  A071007 A071008 A071009 * A071011 A071012 A071013

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, May 19 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 12 07:10 EDT 2022. Contains 356067 sequences. (Running on oeis4.)