A028980 Numbers whose sum of divisors is palindromic.

1, 2, 3, 4, 5, 7, 43, 81, 96, 98, 130, 146, 162, 166, 201, 205, 208, 211, 221, 241, 244, 251, 271, 274, 281, 300, 314, 325, 333, 365, 388, 422, 433, 438, 443, 463, 489, 519, 559, 633, 685, 793, 803, 827, 857, 877, 887, 1376, 1419, 1505, 1548

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Patrick De Geest, World!Of Numbers

Crossrefs

Cf. A000203, A002113.

Programs

Maple

isA028980 := proc(n)
    isA002113(numtheory[sigma](n)) ;
end proc:
for n from 1 to 2000 do
    if isA028980(n) then
        printf("%d,",n) ;
    end if;
end do: # R. J. Mathar, Sep 09 2015

Mathematica

Select[Range[1550],Reverse[x=IntegerDigits[DivisorSigma[1,#]]]==x&] (* Jayanta Basu, Jun 05 2013 *)
Select[Range[1600],PalindromeQ[DivisorSigma[1,#]]&] (* Harvey P. Dale, Jul 20 2021 *)