OFFSET
1,2
COMMENTS
If n is a term of the sequence, then the parallelogram formed by the vectors {n, sigma(n)}, {n+1, sigma(n+1)} has the same area as that of an integral square.
EXAMPLE
Det[{{15, sigma(15)},{16, sigma(16)}}] = Det[{{15,24},{16,31}}] = 9^2, so 15 is a term of the sequence.
MATHEMATICA
f[n_] := Det[{{n, DivisorSigma[1, n]}, {n + 1, DivisorSigma[1, n + 1]}}]; Do[If[f[n] == 0, Print[n]], {n, 1, 10^6}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Jan 30 2002
EXTENSIONS
a(8)-a(27) from Amiram Eldar, Aug 14 2019
STATUS
approved