OFFSET
1,1
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..500
FORMULA
Lim_{n->infinity} a(n)/a(n-1) = e.
It appears that, for most values of n, a(n) = floor(e^(n-1/2) + 7/8) - binomial(n,2). An exception occurs at n = 7; are there more? - Jon E. Schoenfield, Aug 22 2017
No more exceptions found through n = 30000. - Hugo Pfoertner, Aug 25 2017
EXAMPLE
Let s(x) = x*x^(1/x); r(x) = round(s(x));
a(1) = 2:
s(1) = 1,
s(2) = 2.82842712474619...;
r(1) = 1,
r(2) = 3,
r(2) - r(1) = 2;
a(2) = 4:
s(3) = 4.32674871...,
s(4) = 5.6568542...;
r(3) = 4,
r(4) = 6,
r(4) - r(3) = 2;
...
a(19) = 108254817:
s(108254816) = 108254834.49999999422...,
s(108254817) = 108254835.50000000346...;
r(108254816) = 108254834,
r(108254817) = 108254836,
r(108254817) - r(108254816) = 2.
MATHEMATICA
f[n_] := Round[n*n^(1/n)]; g[k_] := f[k] > 1 + f[k-1]; A = Select[Range[2, 5000], g]; Do[AppendTo[A, SelectFirst[Floor[E Last@ A] + Range[1000], g]], {n, 19}]; A (* Giovanni Resta, Aug 21 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Aug 21 2017
STATUS
approved