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A175350 a(n) = the smallest positive integer not yet occurring such that the number of divisors of Sum_{k=1..n} a(k) is exactly n. 4
1, 2, 6, 5, 67, 11, 637, 12, 348, 47, 57913, 26, 472366, 463, 26105, 15, 42488697, 118, 344373650, 136, 2089071, 2496, 30991547417, 7, 332851440, 93936, 3467844, 590, 22845074981535, 31, 183014339639657, 13, 13947373787 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

It seems likely that this is a permutation of the positive integers. Is it?

LINKS

Table of n, a(n) for n=1..33.

FORMULA

Sum_{k=1..n} a(k) = A175351(n).

EXAMPLE

a(4) = k where sigma(a(1) + a(2) + a(3) + k) = sigma(9 + k) = 4. The next number larger than 9 having four divisors is 10. This would give k = 1, which is in the sequence. The next number larger than 10 having four divisors is 14. This would give k = 14 - 9 = 5, which isn't already in the sequence. Therefore, a(4) = 5. - David A. Corneth, Mar 08 2017

MATHEMATICA

a[1]=1; a[n_]:=a[n]=Module[{an=First[Complement[Range[n], a/@Range[n-1]]]},

While[DivisorSigma[0, Sum[a[i], {i, n-1}]+an]!=n||MemberQ[a/@Range[n-1], an], an++];

an]; a/@Range[16] (* Ivan N. Ianakiev, Mar 08 2017 *)

CROSSREFS

Cf. A001055, A175351.

Sequence in context: A281179 A280462 A283475 * A085057 A069113 A009462

Adjacent sequences:  A175347 A175348 A175349 * A175351 A175352 A175353

KEYWORD

nonn

AUTHOR

Leroy Quet, Apr 19 2010

EXTENSIONS

More terms from Farideh Firoozbakht, Mar 20 2010

STATUS

approved

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Last modified June 28 17:16 EDT 2017. Contains 288839 sequences.