A143416 Products of two primes whose difference is a perfect square.

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

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); # 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 A323916 A364202

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