A078575 Sum of divisors of the average of n-th twin prime pair.

7, 12, 28, 39, 72, 96, 168, 195, 216, 280, 288, 372, 546, 508, 468, 560, 744, 720, 576, 840, 840, 1344, 1240, 1152, 1170, 1440, 1860, 1248, 1296, 2016, 2178, 1656, 2184, 2016, 2223, 3024, 2640, 2976, 2340, 3136, 3315, 3024, 2808, 3168, 3072, 4320, 4032

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000203(A014574(n)).

Example

4th twin prime pair = (A001359(4), A006512(4)) = (17,19), hence A014574(4) = 18 with divisors = {1,2,3,6,9,18} therefore a(4) = 1+2+3+6+9+18 = 39.

Mathematica

midQ[n_] := PrimeQ[n-1] && PrimeQ[n+1]; DivisorSigma[1, Select[Range[1500], midQ]] (* Amiram Eldar, Nov 03 2019 *)

Crossrefs

Cf. A000203, A014574, A078574, A078576, A078577.

Sequence in context: A104584 A223417 A224699 * A220036 A330589 A197229

Adjacent sequences: A078572 A078573 A078574 * A078576 A078577 A078578

Keyword

nonn

Author

Reinhard Zumkeller, Nov 29 2002

Status

approved