OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..100000 (terms n = 1..1000 from G. C. Greubel)
EXAMPLE
a(3) = 2 because sigma(1) + sigma(2) + sigma(3) = 1+3+4 > 3.
MAPLE
b:= proc(n) option remember; `if`(n=0, 0,
numtheory[sigma](n)+b(n-1))
end:
a:= proc(n) option remember; local k; for k from
`if`(n=0, 0, a(n-1)) do if b(k)>=n then return k fi od
end:
seq(a(n), n=0..120); # Alois P. Heinz, Sep 12 2019
MATHEMATICA
a[n_] := (k = 1; While[ Total[ DivisorSigma[1, Range[k]]] < n, k++]; k); Table[ a[n], {n, 1, 90}]
Module[{nn=10, ad, th}, ad={#[[1]], #[[2]]}&/@Partition[Accumulate[ DivisorSigma[ 1, Range[nn]]], 2, 1]; th=Thread[{Range[2, nn], ad}]; Join[ {0, 1}, Flatten[Table[#[[1]], #[[2, 2]]-#[[2, 1]]]&/@th]]] (* Harvey P. Dale, Aug 29 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Jan 21 2012
EXTENSIONS
a(0)=0 prepended by Alois P. Heinz, Sep 12 2019
STATUS
approved