OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..2500 from Muniru A Asiru)
MAPLE
with(numtheory): a:=`if`(sigma(n)>=2*n-1 and sigma(n+1)>=2*(n+1)-1, n, NULL): seq(a(n), n=1..120000); # Muniru A Asiru, Jun 26 2018
MATHEMATICA
Select[Range[120000], And[DivisorSigma[1, #] >= 2 #1 - 1, DivisorSigma[1, # + 1] >= 2 (#1 + 1) - 1] &] (* Michael De Vlieger, Jun 29 2018 *)
PROG
(PARI) for(i=1, 1000000, if(sigma(i)>=2*i-1 && sigma(i+1)>=2*i+1, print1(i, ", ")));
(GAP) Filtered([1..120000], n->Sigma(n)>=2*n-1 and Sigma(n+1)>2*(n+1)-1); # Muniru A Asiru, Jun 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Max Alekseyev, Jan 28 2005
STATUS
approved