OFFSET
1,1
COMMENTS
From Robert Israel, Apr 14 2019: (Start)
Numbers k such that A076618(k) is a square.
All terms are odd.
Squarefree terms are k^2-1 for k in A067874.
(End)
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
The prime factors of 35 are 5 and 7 and 5 * 7 + 1 = 36 is a square; so 35 belongs to the sequence.
MAPLE
filter:= n -> issqr(1+convert(numtheory:-factorset(n), `*`)):
select(filter, [$1..10000]); # Robert Israel, Apr 14 2019
MATHEMATICA
ppf[n_] := Apply[Times, Transpose[FactorInteger[n]][[1]]]; Select[Range[2, 10^3], IntegerQ[Sqrt[ppf[ # ] + 1]] &]
PROG
(PARI) isok(n) = my(f=factor(n)); issquare(1+prod(k=1, #f~, f[k, 1])); \\ Michel Marcus, Apr 15 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Jan 04 2004
EXTENSIONS
More terms from Ray Chandler, Jan 05 2004
STATUS
approved