OFFSET
1,3
EXAMPLE
If written as an irregular triangle in which row n has length A026741(n+1) then the first differences in row n are always n (see below).
Triangle begins:
0,
1,3,5,
7,10,
13,17,21,25,29,
33,38,43,
48,54,60,66,72,78,84,
90,97,104,111,
118,126,134,142,150,158,166,174,182,
190,199,208,217,226,
235,245,255,265,275,285,295,305,315,325,335,
345,356,367,378,389,400
MATHEMATICA
a1318[n_] := If[EvenQ[n], n (3 n/2 + 1)/4, (n + 1) (3 n + 1)/8];
a[n_] := DeleteCases[Table[n - a1318[k], {k, 1, n}], _?Negative] // Total;
Array[a, 56] (* Jean-François Alcover, Jun 26 2019 *)
PROG
(Sage)
def A195311(n):
return add(max(0, n-k*(3*k-1)/2)+max(0, n-k*(3*k+1)/2) for k in (1..n))
[A195311(n) for n in (1..56)] # Peter Luschny, Oct 12 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Sep 21 2011
STATUS
approved