A203615 Reversal of sigma(n) equals the sum of the reversals of the divisors of n.

1, 2, 3, 4, 5, 7, 21, 938, 17797, 44045, 87001, 454085, 2217425, 8156450, 8475789, 3293216050, 11130063842, 44662814795, 77084972662

Offset

1,2

Comments

a(20) > 2.34*10^12. - Giovanni Resta, Aug 30 2018

Links

Table of n, a(n) for n=1..19.

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

Cf. A069942, A195144, A203616.

Sequence in context: A065774 A281233 A048459 * A273932 A270831 A063738

Adjacent sequences: A203612 A203613 A203614 * A203616 A203617 A203618

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