OFFSET
1,1
LINKS
Paolo Xausa, Table of n, a(n) for n = 1..14
Philippe Ellia, On the distance between perfect numbers, arXiv:1210.0450 [math.NT], 2012.
Florian Luca, Problem 10711, Amer. Math. Monthly, Vo. 106, No. 2 (1999) p. 166; Can Two Consecutive Numbers Both Be Perfect?, solution by Francis B. Coghlan, ibid., Vol. 108, No. 1 (2001), pp. 80-81.
Florian Luca and Carl Pomerance, On the radical of a perfect number, New York Journal of Math., Vol. 16 (2010), pp. 23-30; alternative link.
Florian Luca and Herman te Riele, phi and sigma: from Euler to Erdős, Nieuw Archief voor Wiskunde, Vol. 12, No. 5 (2011), pp. 31-36.
FORMULA
From Amiram Eldar, May 07 2021: (Start)
a(n) > 1 (Luca, 1999).
a(n) > 4 (Luca and te Riele, 2011). (End)
EXAMPLE
a(1) = 22 because 6 and 28 are the first two perfect numbers, and their difference is 28 - 6 = 22.
MATHEMATICA
Differences[Select[Range[10000], DivisorSigma[1, #] == 2# &]] (* Alonso del Arte, Mar 05 2020 *)
Differences[PerfectNumber[Range[12]]] (* Paolo Xausa, Oct 20 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Apr 18 2008
EXTENSIONS
More terms from Omar E. Pol, Oct 02 2012
STATUS
approved