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A245810
Genus of the complete intersection of two hypersurfaces in P^3.
1
0, 1, 3, 4, 6, 9, 10, 15, 16, 19, 21, 25, 28, 31, 33, 36, 45, 46, 49, 51, 55, 64, 66, 73, 76, 78, 81, 85, 91, 99, 100, 105, 106, 109, 120, 121, 129, 136, 141, 144, 145, 153, 163, 166, 169, 171, 181, 190, 196, 199, 201, 210, 225, 226, 231, 235, 241, 243
OFFSET
1,3
COMMENTS
Integers that can be written as d*e*(d+e-4)/2+1 for positive integers d and e.
LINKS
Jean-François Alcover, Table of n, a(n) for n = 1..10000
MAPLE
filter:= proc(n)
local m, S, Q;
m:= 2*(n-1);
S:= numtheory:-divisors(m);
Q:= map(d ->(4*d-m+sqrt(4*d^3 + 16*d^2 - 8*d*m + m^2))/(2*d), S);
evalb(select(type, Q, posint) <> {})
end proc:
filter(0):= true:
filter(1):= true:
select(filter, [$0..1000]); # Robert Israel, Aug 24 2014
MATHEMATICA
Module[{gmax = 300, g}, Reap[Do[g = d e (d + e - 4)/2 + 1; If[IntegerQ[g], Sow[g]], {d, Ceiling[(3 + Sqrt[1 + 8 gmax])/2]}, {e, d}]][[2, 1]] // Select[#, # <= gmax &]& // Union] (* Jean-François Alcover, Sep 12 2020 *)
CROSSREFS
Sequence in context: A368136 A130904 A034706 * A054686 A005214 A268110
KEYWORD
nonn
AUTHOR
Richard Shadrach, Aug 22 2014
EXTENSIONS
b-file corrected by Jean-François Alcover, Sep 12 2020
STATUS
approved