A230020 Composite numbers n such that sigma(n) - reversal(n) = 1.

9599, 31874, 93689, 932639, 1367991, 13451831, 309173753, 99148830299

Offset

1,1

Comments

It is obvious that palindromic primes (palprimes) are all prime solutions of the equation sigma(x)-reversal(x) = 1. The next term is greater than 73*10^7.

a(9) > 10^12. - Giovanni Resta, Dec 14 2013

Links

Table of n, a(n) for n=1..8.

Example

sigma(9599) = sigma(29*331) = 30*332 = 9960 = reverse(9599)+1.

Mathematica

Do[a=FromDigits[Reverse[IntegerDigits[n]]]; If[a>n && DivisorSigma[1, n] -a == 1, Print[n]], {n, 730000000}]

Crossrefs

Cf. A000203, A002385, A004086, A130000.

Sequence in context: A250761 A038825 A038814 * A034626 A031596 A236715

Adjacent sequences: A230017 A230018 A230019 * A230021 A230022 A230023

Keyword

nonn,base,more

Author

Farideh Firoozbakht, Nov 26 2013

Extensions

a(8) from Giovanni Resta, Dec 14 2013

Status

approved