A281879 Non-palindromic numbers k such that sigma(k) | sigma(R(k)), where R(k) is the digit reversal of k.

15, 16, 17, 59, 129, 165, 176, 187, 205, 273, 276, 299, 429, 446, 478, 528, 599, 825, 1034, 1043, 1135, 1209, 1239, 1515, 1561, 1565, 1616, 1651, 1665, 1717, 1776, 1887, 2086, 2165, 2178, 2255, 2455, 2515, 2618, 2739, 2829, 3489, 4008, 4064, 4475, 4604, 5346, 5795

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..500

Paolo P. Lava, First 250 terms with the ratio sigma(R(k))/sigma(k)

Example

a(1) = 15 because sigma(51) / sigma(15) = 72 / 24 = 3;
a(2) = 16 because sigma(61) / sigma(16) = 62 / 31 = 2;
a(3) = 17 because sigma(71) / sigma(17) = 72 / 18 = 4.

Maple

with(numtheory): T:=proc(w) local x, y, z; x:=w; y:=0;
for z from 1 to ilog10(x)+1 do y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end:
P:=proc(q) local n; for n from 1 to q do
if n<>T(n) then if type(sigma(T(n))/sigma(n), integer) then print(n); fi; fi; od; end: P(10^6);

Mathematica

Select[Range[6000], !PalindromeQ[#]&&Mod[DivisorSigma[1, IntegerReverse[#]], DivisorSigma[ 1, #]] ==0&] (* Harvey P. Dale, Dec 19 2023 *)

Crossrefs

Cf. A000203, A004086, A085329, A281880.

Sequence in context: A358043 A090461 A138598 * A354626 A114841 A031168

Adjacent sequences: A281876 A281877 A281878 * A281880 A281881 A281882

Keyword

nonn,easy,base

Author

Paolo P. Lava, Feb 01 2017

Status

approved