OFFSET
1,2
COMMENTS
a(20) > 2.34*10^12. - Giovanni Resta, Aug 30 2018
EXAMPLE
n=17797. Divisors: 1, 13, 37, 481, 1369, 17797.
Sum of the reversals of the divisors: 1+31+73+184+9631+79771=89691.
Sigma(17797)=19698 and its reversal is 89691.
n=454085. Divisors: 1, 5, 197, 461, 985, 2305, 90817, 454085.
Sum of the reversals of the divisors: 1+5+791+164+589+5032+71809+580454=658845.
Sigma(454085)=548856 and its reversal is 658845.
MAPLE
with(numtheory);
Rev:=proc(n)
local a, i, k;
i:=convert(n, base, 10); a:=0;
for k from 1 to nops(i) do a:=a*10+i[k]; od;
a;
end:
P:=proc(s)
local a, b, c, j, pfs;
for j from 1 to s do
b:=divisors(j); a:=0;
for c from 1 to nops(b) do a:=a+Rev(b[c]); od;
if Rev(sigma(j))=a then print(j); fi;
od;
end:
P(10000000);
MATHEMATICA
Select[Range[33*10^8], Total[IntegerReverse/@Divisors[#]] == IntegerReverse[ DivisorSigma[ 1, #]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 09 2018 *)
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Paolo P. Lava, Jan 20 2012
EXTENSIONS
a(13)-a(16) from Donovan Johnson, Jan 29 2012
a(17)-a(19) from Giovanni Resta, Aug 30 2018
STATUS
approved