OFFSET
1,2
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
MATHEMATICA
Select[Range[25000], AllTrue[{Sqrt[1+8*DivisorSigma[0, #]], Sqrt[ 1+ 8*DivisorSigma[ 1, #]]}, OddQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Jun 01 2019 *)
PROG
(PARI) c=0; for(n=1, 15891631, s=sigma(n); s2=2*s; r=sqrtint(s2); if(r*(r+1)<>s2, next); nd=numdiv(n); nd2=2*nd; r=sqrtint(nd2); if(r*(r+1)==nd2, c++; write("b070996.txt", c " " n))) /* Donovan Johnson, Mar 10 2013 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, May 18 2002
STATUS
approved