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A284495 a(n) is the least number such that d(a(n)) = d(R(a(n)))/n, where R(n) is the digit reverse of n and d(n) is the number of divisors of n. 3
1, 19, 23, 213, 211, 293, 2519, 827, 2129, 2593, 23259, 2707, 253653, 21143, 21927, 21799, 2177667, 21529, 8239969, 25579, 21757, 232153, 67719697, 210229, 2112597, 2171101, 217519, 211879, 27857904077, 211007, 25135138387, 219059, 2914689, 4878977, 4646637, 230693 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..36.

FORMULA

Solutions of the equation A000005(n) = A000005(A004086(n))/n.

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

Cf. A000005, A004086, A284496 - A284498.

Sequence in context: A107185 A240585 A226607 * A160077 A076353 A297575

Adjacent sequences:  A284492 A284493 A284494 * A284496 A284497 A284498

KEYWORD

nonn,base

AUTHOR

Paolo P. Lava, Mar 28 2017

EXTENSIONS

a(19)-a(36) from Giovanni Resta, Mar 29 2017

STATUS

approved

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Last modified March 23 04:46 EDT 2019. Contains 321422 sequences. (Running on oeis4.)