OFFSET
1,4
COMMENTS
It is conjectured that A071640(n)/n -> 1/2. - Benoit Cloitre
a(6671) < 0. - Peter Luschny, Oct 05 2011
MAPLE
A086144 := proc(n) option remember; if n=1 then 1 else
if combinat[numbpart](n) mod 2 = 1 then 1 else -1 fi;
MATHEMATICA
a071640[n_] := Sum[Mod[PartitionsP[i], 2], {i, 1, n}];
a[n_] := 2 a071640[n] - n;
Array[a, 100] (* Jean-François Alcover, Jun 11 2019 *)
PROG
(PARI) a(n) = my(x='x+O('x^(n+1)), p = 1/eta(x)); sum(i=1, n, (1-(-1)^(polcoeff(p, i)))) - n; \\ Michel Marcus, Jun 11 2019
CROSSREFS
KEYWORD
sign
AUTHOR
Benoit Cloitre, Sep 06 2003
EXTENSIONS
Erroneous data for n>55 replaced, keyword sign added by Peter Luschny, Oct 05 2011
STATUS
approved