OFFSET
1,2
COMMENTS
Positive numbers k == 0 or 1 (mod 4), excluding k=4.
Essentially the same as A042948 (except 4 is not in this sequence).
The set {s(i)} is closed under multiplication. - Lekraj Beedassy, Jan 21 2005
LINKS
O. P. Lossers, Solution to problem 10454: Amenable Numbers, Amer. Math. Monthly Vol. 105 No. 4 April 1998.
Eric Weisstein's World of Mathematics, Amenable Number
Wikipedia, Amenable number
Index entries for linear recurrences with constant coefficients, signature (1, 1, -1).
FORMULA
From Colin Barker, Jan 26 2012: (Start)
a(n) = a(n-1) + a(n-2) - a(n-3), n > 4.
G.f.: x*(1+3*x)*(1+x-x^2)/(1-x-x^2+x^3). (End)
EXAMPLE
5 and 8, for instance, are in the sequence because we have 5 = 1-1+1-1+5 = 1*(-1)*1*(-1)*5 and 8 = 1-1+1-1+1+1+2+4 = 1*(-1)*1*(-1)*1*1*2*4.
CROSSREFS
KEYWORD
nonn
AUTHOR
Lekraj Beedassy, Jan 07 2005
EXTENSIONS
More terms from David W. Wilson, Jan 24 2005
STATUS
approved