A056700 -id:A056700 - cp's OEIS frontend

A084831 Numbers n such that sum of odd divisors and sum of even divisors are both palindromic.

1, 2, 3, 4, 5, 6, 7, 43, 81, 86, 162, 201, 205, 211, 221, 241, 251, 271, 281, 325, 333, 344, 365, 422, 433, 443, 463, 482, 489, 519, 559, 633, 650, 685, 730, 793, 803, 827, 857, 866, 877, 886, 887, 1419, 1505, 1841, 2021, 2111, 2221, 2305, 2441, 2551, 2561, 2611

Offset: 1

Jason Earls, Jun 05 2003

Primes of form 2*10^n + R(n) (A056700) and 2/9*(-1+10^n)-1 (A084832) are members.

			a(11)=162 because sum of even divisors is 242 and sum of odd divisors is 121.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A000593, A056700, A084832.

sodQ[n_]:=Module[{dn=Divisors[n],o,e},o=IntegerDigits[Total[Select[ dn,OddQ]]]; e=IntegerDigits[Total[Select[dn,EvenQ]]]; o== Reverse[o] && e==Reverse[e]]; Select[Range[3000],sodQ] (* Harvey P. Dale, Feb 27 2013 *)

A068814 Primes with a 2 followed by (possibly zero) 1's.

Original entry on oeis.org

2, 211, 2111, 2111111111111, 2111111111111111111, 211111111111111111111111, 2111111111111111111111111111111111111111111111111111111111, 211111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

Offset: 1

Amarnath Murthy, Mar 07 2002

nonn

Primes of the form (19*10^n-1)/9.

The next term (a(9)) has 544 digits. Harvey P. Dale, Sep 28 2015

Makoto Kamada, Prime numbers of the form 211...11.
Index entries for primes involving repunits

Cf. A056700.

Select[Table[FromDigits[Join[{2},PadRight[{},n,1]]],{n,0,130}],PrimeQ] (* Harvey P. Dale, Sep 28 2015 *)

for(n=0,200, if(isprime(2*10^n+(10^(n)-1)/9)==1,print1(2*10^n+(10^(n)-1)/9,",")))

a(n) = (19*10^A056700(n)-1)/9.

More terms from Benoit Cloitre, Mar 09 2002

Edited by Ray Chandler, Feb 03 2012

cp's OEIS Frontend

A084831 Numbers n such that sum of odd divisors and sum of even divisors are both palindromic.

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