OFFSET
1,3
COMMENTS
Is the sequence increasing? (checked to n=5000).
FORMULA
a(n)=sum{k_i is a generalized pentagonal, (-1)^(floor((i+1)/2))*(n-k)}
EXAMPLE
a(10) is given via the expansion part(10)=part(9)+part(8)-part(5)-part(3), so in this sequence a(10)=9+8-5-3=9.
PROG
(PARI) { gp=vecsort(vector(20, i, x=10-i; x*(3*x-1)/2)); for (n=1, 50, s=0; i=1; while (n-gp[i+1]>0, s-=(-1)^(floor((i+1)/2))*(n-gp[i+1]); i++); print1(", "s)) }
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon Perry, Sep 12 2003
STATUS
approved