OFFSET
1,2
COMMENTS
It seems likely that this is a permutation of the positive integers. Is it?
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
KEYWORD
nonn
AUTHOR
Leroy Quet, Apr 19 2010
EXTENSIONS
More terms from Farideh Firoozbakht, Mar 20 2010
STATUS
approved