OFFSET
1,2
FORMULA
a(n) is asymptotic to 4n^2/15; a(n)=4n^2/15 if n is of the form 30*(2k+1) hence a(60k+30) = 1800*(2k+1)^2
EXAMPLE
a(8) = a(7) + ( (-1)^a(7)*a(7)) mod 8 = 13 + (- 13) mod 8 = 13 + 3 = 16
MATHEMATICA
RecurrenceTable[{a[1]==1, a[n]==a[n-1]+Mod[(-1)^a[n-1] a[n-1], n]}, a, {n, 60}] (* Harvey P. Dale, Nov 09 2011 *)
PROG
(PARI) a(n)=a(n-1)+((-1)^a(n-1)*a(n-1))%n
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Nov 07 2002
STATUS
approved