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A045636 Numbers of the form p^2 + q^2, with p and q primes. 23
8, 13, 18, 29, 34, 50, 53, 58, 74, 98, 125, 130, 146, 170, 173, 178, 194, 218, 242, 290, 293, 298, 314, 338, 365, 370, 386, 410, 458, 482, 530, 533, 538, 554, 578, 650, 698, 722, 818, 845, 850, 866, 890, 962, 965, 970, 986, 1010, 1058, 1082, 1130, 1202, 1250 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A045698(a(n)) > 0. - Reinhard Zumkeller, Jul 29 2012

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

Index entries for sequences related to sums of squares

FORMULA

Characteristic function for values of a(n) = sgn(sum_{i=2..floor(n/2)}(pi((sqrt(i)))-pi(sqrt(i)-1)) * (pi((sqrt(n-i)))-pi((sqrt(n-i))-1)) *(1-ceil(sqrt(i))+floor(sqrt(i))) * (1-ceil(sqrt(n-i))+floor(sqrt(n-i)))). - Wesley Ivan Hurt, Jun 12 2013

EXAMPLE

18 belongs to the sequence because it can be written as 3^2 + 3^2.

MATHEMATICA

q=13; imax=Prime[q]^2; Select[Union[Flatten[Table[Prime[x]^2+Prime[y]^2, {x, q}, {y, x}]]], #<=imax&] (* Vladimir Joseph Stephan Orlovsky, Apr 20 2011 *)

With[{nn=60}, Take[Union[Total/@(Tuples[Prime[Range[nn]], 2]^2)], nn]] (* Harvey P. Dale, Jan 04 2014 *)

PROG

(PARI) list(lim)=my(p1=vector(primepi(sqrt(lim-4)), i, prime(i)^2), t, p2=List()); for(i=1, #p1, for(j=i, #p1, t=p1[i]+p1[j]; if(t>lim, break, listput(p2, t)))); vecsort(Vec(p2), , 8) \\ Charles R Greathouse IV, Jun 21 2012

(Haskell)

import Data.List (findIndices)

a045636 n = a045636_list !! (n-1)

a045636_list = findIndices (> 0) a045698_list

-- Reinhard Zumkeller, Jul 29 2012

CROSSREFS

A214723 is a subsequence. Complement: A214879.

Cf. A214511 (least number having n orderless representations as p^2 + q^2).

Sequence in context: A224251 A006619 A023487 * A214723 A022954 A070130

Adjacent sequences:  A045633 A045634 A045635 * A045637 A045638 A045639

KEYWORD

nonn,nice

AUTHOR

Felice Russo

STATUS

approved

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Last modified May 25 22:17 EDT 2019. Contains 323576 sequences. (Running on oeis4.)