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 A086989 Sum of even-indexed divisors of n. 1
 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 (list; graph; refs; listen; history; text; internal format)
 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 A349789 Adjacent sequences: A086986 A086987 A086988 * A086990 A086991 A086992 KEYWORD nonn AUTHOR Jon Perry, Jul 27 2003 STATUS approved

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Last modified September 22 01:59 EDT 2023. Contains 365503 sequences. (Running on oeis4.)