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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A143416 Products of two primes whose difference is a perfect square. 2
6, 21, 22, 57, 77, 161, 166, 201, 205, 221, 301, 309, 377, 437, 454, 497, 517, 597, 745, 749, 886, 901, 1057, 1357, 1457, 1461, 1469, 1517, 1577, 1841, 1961, 2021, 2041, 2077, 2182, 2317, 2361, 2537, 2701, 3046, 3097, 3397, 3437, 3497, 3737, 3841, 3901 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..47.

EXAMPLE

57=19*3 and 19-3=16=4^2

MAPLE

with(numtheory): a:=proc(n) if bigomega(n)=2 and nops(factorset(n))=2 and type(sqrt(factorset(n)[2]-factorset(n)[1]), integer)=true then n else end if end proc: seq(a(n), n=1..4000); [From Emeric Deutsch, Aug 16 2008]

MATHEMATICA

Take[ Sort[ Times @@@ Select[ Subsets[ Array[ Prime, 310], {2}], IntegerQ[ Sqrt[ #[[2]] - #[[1]] ]] &]], 48] (* Robert G. Wilson v *)

CROSSREFS

Cf. A141755.

Sequence in context: A184291 A102993 A276803 * A273787 A229498 A164698

Adjacent sequences:  A143413 A143414 A143415 * A143417 A143418 A143419

KEYWORD

nonn

AUTHOR

David Spector (spectord(AT)ccsu.edu), Aug 13 2008

EXTENSIONS

Extended by Emeric Deutsch, Aug 16 2008

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified August 23 01:14 EDT 2017. Contains 290953 sequences.