OFFSET
1,1
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..10000
EXAMPLE
For n=11, 11+12 = 23, sigma(23) = 24; sigma(11*12) = sigma(132) = 336 and 24|336.
MAPLE
for n from 1 to 500 do if numtheory[sigma](n*(n+1)) mod numtheory[sigma](2*n+1) = 0 then printf("%d, ", n); fi; od: # R. J. Mathar, Dec 04 2008
with(numtheory): a := proc (n) if type(sigma(n^2+n)/sigma(2*n+1), integer) = true then n else end if end proc: seq(a(n), n = 1 .. 400); # Emeric Deutsch, Dec 03 2008
MATHEMATICA
Select[Range[335], Mod @@ DivisorSigma[1, {#^2 + #, 2 # + 1}] == 0 &] (* Michael De Vlieger, Dec 14 2019 *)
PROG
(PARI) for(k=1, 335, if(!(sigma(k^2+k)%sigma(2*k+1)), print1(k, ", "))) \\ Hugo Pfoertner, Dec 10 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot, Nov 29 2008
EXTENSIONS
Corrected and extended by Emeric Deutsch and R. J. Mathar, Dec 03 2008
STATUS
approved