OFFSET
0,2
FORMULA
a(n) = a(n-1) + a(n - t(n)) where t(n) = [(sqrt(8n + 17) - 3)/2] for n>0, with a(0)=1.
EXAMPLE
First differences (A131771) begin:
[1,1,2,4,4,8,12,20,20,32,52,72,104,104,156,228,332,436,592,592,...].
Second differences (A131772) begin:
[1,0,1,2,0,4,4,8,0,12,20,20,32,0,52,72,104,104,156,0,228,332,436,592,592,...]
which equals the first differences with zeros inserted at positions {m*(m+1)/2, m>=0}.
PROG
(PARI) a(n)=if(n==0, 1, a(n-1)+a(n-(sqrtint(8*n+17)-3)\2))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 14 2007
STATUS
approved