OFFSET
0,1
COMMENTS
Odd-indexed terms are equal to a square or to a square plus one. - Giovanni Resta, Apr 28 2017
LINKS
Paolo P. Lava and Giovanni Resta, Table of n, a(n) for n = 0..1000 (first 150 terms from Paolo P. Lava)
EXAMPLE
a(9) = 325 because 324 has 15 divisors (1, 2, 3, 4, 6, 9, 12, 18, 27, 36, 54, 81, 108, 162, 324), 325 has 6 divisors (1, 5, 13, 25, 65, 325) and 15 - 6 = 9.
MAPLE
with(numtheory): P:=proc(q) local a, b, k, v; v:=array(0..200);
for k from 0 to 200 do v[k]:=0; od; a:=1;
for k from 2 to q do b:=tau(k); if v[abs(b-a)]=0 then v[abs(b-a)]:=k; fi; a:=b; od; k:=0;
while v[k]>0 do print(v[k]); k:=k+1; od; print(); end: P(3*10^5);
MATHEMATICA
s = DivisorSigma[0, #] &@ Range[10^6]; 1 + First /@ Values@ KeySort@ PositionIndex@ Flatten@ Map[Abs@ Differences@ # &, Partition[s, 2, 1]] (* Michael De Vlieger, Apr 26 2017, Version 10 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Apr 26 2017
STATUS
approved