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 A070038 a(n) = sum of divisors of n that are at least sqrt(n). 39
 1, 2, 3, 6, 5, 9, 7, 12, 12, 15, 11, 22, 13, 21, 20, 28, 17, 33, 19, 35, 28, 33, 23, 50, 30, 39, 36, 49, 29, 61, 31, 56, 44, 51, 42, 81, 37, 57, 52, 78, 41, 84, 43, 77, 69, 69, 47, 108, 56, 85, 68, 91, 53, 108, 66, 106, 76, 87, 59, 147, 61, 93, 93, 120, 78, 132, 67, 119, 92 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) = n iff n is not a composite number. Sum of a subset of all divisors of n, not including complementary divisors of any term. LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 EXAMPLE a(20) = 35: the divisors of 20 are 1,2,4,5,10 and 20. a(20) = 5 + 10 + 20 = 35. a(96) = 228 = 96 + 48 + 32 + 24 + 16 + 12 (sum of an even number of divisors); a(225) = 385 = 225 + 75 + 45 + 25 + 15 (sum of an odd number of divisors). MAPLE with(numtheory):for n from 1 to 200 do c[n] := 0:d := divisors(n):for i from 1 to nops(d) do if d[i]>=n^.5 then c[n] := c[n]+d[i]:fi:od:od:seq(c[i], i=1..200); MATHEMATICA Table[Plus @@ Select[Divisors[n], # >= Sqrt[n] &], {n, 1, 70}] PROG (Sage) [sum(k for k in divisors(n) if k^2>=n) for n in range (1, 70)] # Giuseppe Coppoletta, Jan 21 2015 (PARI) a(n) = sumdiv(n, d, d*(d^2>=n)); \\ Michel Marcus, Jan 22 2015 CROSSREFS Cf. A038548, A000203, A000005, A070039, A056924, A072500, A066839. Sequence in context: A257011 A144652 A035493 * A328638 A327420 A119790 Adjacent sequences:  A070035 A070036 A070037 * A070039 A070040 A070041 KEYWORD nonn AUTHOR Labos Elemer, Apr 19 2002 STATUS approved

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Last modified May 16 21:28 EDT 2021. Contains 343951 sequences. (Running on oeis4.)