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A203615 Reversal of sigma(n) equals the sum of the reversals of the divisors of n. 1
1, 2, 3, 4, 5, 7, 21, 938, 17797, 44045, 87001, 454085, 2217425, 8156450, 8475789, 3293216050, 11130063842, 44662814795, 77084972662 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 19 22:14 EDT 2019. Contains 325168 sequences. (Running on oeis4.)