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A323441
Numbers equal to the sum of the numbers between two of their divisors.
1
12, 30, 60, 90, 108, 180, 234, 240, 390, 408, 420, 462, 480, 490, 630, 756, 840, 880, 900, 945, 1122, 1218, 1248, 1430, 1500, 1512, 1560, 1584, 1998, 2070, 2100, 2310, 2460, 2520, 2652, 2660, 2970, 3306, 3330, 3528, 3780, 3960, 4004, 4032, 4134, 4140, 4275, 4788
OFFSET
1,1
COMMENTS
A303556 is a subsequence of this sequence.
LINKS
EXAMPLE
Divisors of 12 are 1, 2, 3, 4, 6, 12 and the sum of the numbers between 2 and 6 is 3 + 4 + 5 = 12.
Divisors of 108 are 1, 2, 3, 4, 6, 9, 12, 18, 27, 36, 54, 108 and the sum of the numbers between 9 and 18 is 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 = 108.
MAPLE
with(numtheory): P:=proc(n) local a, j, k; a:=sort([op(divisors(n))]);
for j from 1 to nops(a)-1 do for k from j+1 to nops(a) do
if n=((a[k]-1)*a[k]-a[j]*(a[j]+1))/2 then RETURN(n); fi;
od; od; end: seq(P(i), i=2..10^4);
MATHEMATICA
Select[Range[5000], MemberQ[Union@ Map[Total@ Range[#1 + 1, #2 - 1] & @@ # &, Subsets[Divisors@ #, {2}]], #] &] (* Michael De Vlieger, Jan 18 2019 *)
CROSSREFS
Sequence in context: A286497 A086830 A084699 * A064483 A375718 A365277
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Jan 15 2019
STATUS
approved