A086989 Sum of even-indexed divisors of n.

0, 2, 3, 2, 5, 8, 7, 10, 3, 12, 11, 18, 13, 16, 18, 10, 17, 26, 19, 27, 24, 24, 23, 38, 5, 28, 30, 37, 29, 47, 31, 42, 36, 36, 40, 33, 37, 40, 42, 57, 41, 64, 43, 57, 57, 48, 47, 78, 7, 62, 54, 67, 53, 80, 60, 79, 60, 60, 59, 104, 61, 64, 75, 42, 70, 96, 67, 87, 72, 93, 71, 122, 73

Offset

1,2

Comments

a(p)=p iff p prime.

Links

Table of n, a(n) for n=1..73.

Example

10 has divisors 1,2,5 and 10. The even indices yield 2 and 10, so a(10)=12.

Mathematica

Prepend[Table[Total[Transpose[Partition[Divisors[n], 2]][[2]]], {n, 2, 100}], 0]  (* Harvey P. Dale, Jan 17 2011 *)

Prog

(PARI) for (n=1, 100, s=0; c=0; fordiv(i=n, i, c++; if (c%2==0, s+=i)); print1(", "s))

Crossrefs

Cf. A086988.

Sequence in context: A064939 A248012 A151549 * A110642 A079535 A367859

Adjacent sequences: A086986 A086987 A086988 * A086990 A086991 A086992

Keyword

nonn

Author

Jon Perry, Jul 27 2003

Status

approved