OFFSET
1,1
COMMENTS
It seems that for all n, a(n)/n <= 2019/62. [Farideh Firoozbakht, Aug 22 2014]
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=1 and m = 2 and 3 phi(m+1) != sigma(m-1), but for m=4 phi(m+1) = sigma(m-1). Thus a(1) = 4.
MAPLE
with(numtheory):
a:= proc(n) local m;
for m from n+1 while phi(m+n)<>sigma(m-n) do od; m
end:
seq(a(n), n=1..80); # Alois P. Heinz, Aug 05 2013
MATHEMATICA
a[m_]:=(For[n=m+1, DivisorSigma[1, n-m]!=EulerPhi[n+m], n++]; n); Table[a[n], {n, 70}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Aug 02 2013
STATUS
approved