A086988 Sum of odd indexed divisors of n.

1, 1, 1, 5, 1, 4, 1, 5, 10, 6, 1, 10, 1, 8, 6, 21, 1, 13, 1, 15, 8, 12, 1, 22, 26, 14, 10, 19, 1, 25, 1, 21, 12, 18, 8, 58, 1, 20, 14, 33, 1, 32, 1, 27, 21, 24, 1, 46, 50, 31, 18, 31, 1, 40, 12, 41, 20, 30, 1, 64, 1, 32, 29, 85, 14, 48, 1, 39, 24, 51, 1, 73, 1, 38, 31, 43, 12, 56, 1, 69

Offset

1,4

Comments

a(p) = 1 iff p is prime or p=1.

Links

Table of n, a(n) for n=1..80.

Example

10 has divisors 1,2,5 and 10. The odd-indexed divisors are 1 and 5, so a(10)=6.

Mathematica

Table[Total[Transpose[Partition[Divisors[n], 2, 2, 1]][[1]]], {n, 80}]  (* Harvey P. Dale, Apr 21 2011 *)

Prog

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

Crossrefs

Cf. A000005, A086989.

Sequence in context: A023138 A194704 A108170 * A010132 A254247 A216606

Adjacent sequences: A086985 A086986 A086987 * A086989 A086990 A086991

Keyword

nonn

Author

Jon Perry, Jul 27 2003

Status

approved