login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A257408 Values of n such that there is exactly 1 solution to x^2 - y^2 = n with x > y >= 0. 11
1, 3, 4, 5, 7, 8, 11, 12, 13, 17, 19, 20, 23, 28, 29, 31, 37, 41, 43, 44, 47, 52, 53, 59, 61, 67, 68, 71, 73, 76, 79, 83, 89, 92, 97, 101, 103, 107, 109, 113, 116, 124, 127, 131, 137, 139, 148, 149, 151, 157, 163, 164, 167, 172, 173, 179, 181, 188, 191, 193 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The terms a(1)=1 and a(3)=4 are the only squares in this sequence. - M. F. Hasler, Apr 22 2015

LINKS

Colin Barker, Table of n, a(n) for n = 1..1500

EXAMPLE

13 is in the sequence because there is only 1 solution to x^2 - y^2 = 13, namely (x,y) = (7,6).

MATHEMATICA

r[n_] := Reduce[x^2 - y^2 == n && x > y >= 0, {x, y}, Integers]; Reap[For[n = 1, n < 200, n++, If[r[n][[0]] === And, Print[n]; Sow[n]]]][[2, 1]] (* Jean-Fran├žois Alcover, Apr 22 2015 *)

PROG

(PARI) is(n)=A034178(n)==1 \\ M. F. Hasler, Apr 22 2015

CROSSREFS

Cf. A257409-A257417.

Cf. A034178.

Sequence in context: A173001 A325130 A047500 * A131613 A138494 A285531

Adjacent sequences:  A257405 A257406 A257407 * A257409 A257410 A257411

KEYWORD

nonn

AUTHOR

Colin Barker, Apr 22 2015

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 14 17:32 EST 2019. Contains 329979 sequences. (Running on oeis4.)