login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A300794
Least number k that is expressible as the sum of 2 abundant numbers in n ways.
2
24, 36, 48, 66, 60, 84, 90, 96, 108, 126, 120, 150, 144, 174, 168, 364, 180, 234, 392, 228, 216, 252, 240, 294, 264, 288, 330, 342, 312, 300, 336, 402, 390, 372, 700, 396, 360, 450, 408, 432, 848, 522, 456, 492, 420, 558, 546, 516, 594, 504, 480, 552, 642, 540
OFFSET
1,1
LINKS
EXAMPLE
a(1) = 24 = 12 + 12;
a(2) = 36 = 12 + 24 = 18 + 18;
a(3) = 48 = 12 + 36 = 18 + 30 = 24 + 24;
a(4) = 66 = 12 + 54 = 18 + 48 = 24 + 42 = 30 + 36,
etc.
MAPLE
with(numtheory); P:=proc(q) local a, b, i, j, n, v; v:=array(1..10^4);
for n from 1 to 10^4 do v[n]:=0; od; a:=0;
for n from 1 to q do b:=0; for i from 1 to trunc(n/2) do
if sigma(i)>2*i and sigma(n-i)>2*(n-i) then b:=b+1; fi; od;
if b=a+1 then a:=b; print(n); j:=1;
while v[b+j]>0 do a:=b+j; print(v[b+j]); j:=j+1; od; else if b>a+1 then
if v[b]=0 then v[b]:=n; fi; fi; fi; od; end: P(10^6);
MATHEMATICA
a[n_] := Block[{t=0, lim=0, ab={}}, While[t == 0, ab = Join[ab, Select[ Range[lim, lim + 499], DivisorSigma[1, #] > 2 # &]]; t = SelectFirst[ Range[lim, lim + 499], Length[ IntegerPartitions[#, {2}, ab]] == n &, 0]; lim += 500]; t]; Array[a, 54] (* Giovanni Resta, Mar 14 2018 *)
CROSSREFS
Cf. A005101.
Sequence in context: A067766 A376445 A306776 * A327945 A078347 A187516
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Mar 13 2018
STATUS
approved