A073839 Sum of the composite numbers between n and 2n (both inclusive).

0, 4, 10, 18, 33, 45, 53, 84, 94, 105, 138, 162, 201, 256, 272, 289, 340, 411, 431, 510, 532, 555, 624, 672, 747, 825, 853, 937, 1024, 1084, 1116, 1243, 1342, 1377, 1482, 1519, 1557, 1708, 1825, 1866, 1989, 2073, 2202, 2377, 2423, 2561, 2702, 2893, 2943

Offset: 1

Author

Amarnath Murthy, Aug 13 2002

Keywords

• nonn

Comments

a(n) is the sum of A075084(n) composite numbers (A002808). - Michel Marcus, Aug 26 2015

Examples

			a(6) = 6+8+9+10+12 = 45.
		

Crossrefs

Cf. A002808, A073840, A075084.

Programs

Maple

for n from 1 to 150 do l := 0:for j from n to 2*n do if not isprime(j) then l := l+j:fi:od:a[n] := l:od:a[1] := 0:seq(a[j],j=1..150);

Mathematica

cs[x_] := Flatten[Position[Table[PrimeQ[j], {j, x, 2*x}], False]]+x-1; sucs[x_] := Apply[Plus, cs[x]]; Table[sucs[w], {w, 1, 128}]
Join[{0}, Table[Plus @@ Select[Range[n, 2 n], ! PrimeQ[#] &], {n, 2, 49}]] (* Jayanta Basu, Aug 12 2013 *)

PARI

a(n) = my(s=0); forcomposite (c=n, 2*n, s+=c); s; \\ Michel Marcus, Aug 26 2015

Extensions

More terms from Sascha Kurz and Labos Elemer, Aug 14 2002