OFFSET
1,2
EXAMPLE
d(1) = 1. Its digit reverse is again 1 and d(1) = 1 = 1 * 1;
d(19) = 2 and d(91) = 4 = 2 * 2;
d(23) = 2 and d(32) = 6 = 3 * 2;
d(213) = 4 and d(312) = 16 = 4 * 4; etc.
MAPLE
with(numtheory): R:=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 k, n; for k from 1 to q do for n from 2 to q do
if k*tau(n)=tau(R(n)) then print(n); break; fi; od; od; end: P(10^9);
MATHEMATICA
rev[n_] := FromDigits@ Reverse@ IntegerDigits@ n; d[n_] := DivisorSigma[0, n]; a[n_] := Block[{k}, For[k=1, d@ rev@ k != n d@ k, k++]; k]; Array[a, 16] (* Giovanni Resta, Mar 29 2017 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava, Mar 28 2017
EXTENSIONS
a(19)-a(36) from Giovanni Resta, Mar 29 2017
STATUS
approved