OFFSET
1,2
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
N:= 2000: # for terms <= N
Res:= NULL:
for m from 1 to floor(sqrt(N)) by 2 do
sm:= numtheory:-sigma(m^2);
for k from 1 to floor(log[2](N/sm+1)) do
v:= sm*(2^k-1);
if v <= N then Res:= Res, v; count:= count+1 fi;
od
od:
sort([Res]); # Robert Israel, Jan 14 2020
MATHEMATICA
Sort@ Select[DivisorSigma[1, Range@ 2000], OddQ[#] && # < 2000 &] (* Giovanni Resta, Jan 08 2020 *)
PROG
(PARI) list(lim)=select(k->k<=lim, vecsort(apply(sigma, concat(vector(sqrtint(lim\1), i, i^2), vector(sqrtint(lim\2), i, 2*i^2))))) \\ Charles R Greathouse IV, Feb 15 2013 [originally added in A152677]
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Jan 08 2020
STATUS
approved