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

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A020668 Numbers of the form x^2 + 4*y^2. 7
0, 1, 4, 5, 8, 9, 13, 16, 17, 20, 25, 29, 32, 36, 37, 40, 41, 45, 49, 52, 53, 61, 64, 65, 68, 72, 73, 80, 81, 85, 89, 97, 100, 101, 104, 109, 113, 116, 117, 121, 125, 128, 136, 137, 144, 145, 148, 149, 153, 157, 160, 164, 169, 173, 180, 181, 185, 193, 196, 197, 200, 205, 208 (list; graph; refs; listen; history; internal format)
OFFSET

1,3

COMMENTS

Numbers that can be expressed as both the sum of two squares and the difference of two squares; the intersection of sequences A001481 and A042965. - T. D. Noe (noe(AT)sspectra.com), Feb 05 2003

A004531(n) is nonzero if and only if n is of the form x^2 + 4*y^2. - Michael Somos, Jan 05 2012

CROSSREFS

Cf. A001481, A042965.

Sequence in context: A188085 A206554 A073320 * A020934 A094004 A067271

Adjacent sequences:  A020665 A020666 A020667 * A020669 A020670 A020671

KEYWORD

easy,nonn

AUTHOR

David W. Wilson (davidwwilson(AT)comcast.net)

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 17 14:19 EST 2012. Contains 206038 sequences.