The OEIS is supported by the many generous donors to the OEIS Foundation.

Composite numbers n such that sum of the proper divisors of n is a power of 10.

0

`%I #16 Mar 21 2014 20:07:06
`

`%S 14,124,194,1324,1994,13324,133324,1130324,1333324,13333324,62496048,
`

`%T 133333324,92782317392
`

`%N Composite numbers n such that sum of the proper divisors of n is a power of 10.
`

`%C Composite numbers n such that reversal(sigma(n)-n))=1.
`

`%C If n is prime then sum of the proper divisors of n is 10^0.
`

`%C If m is a natural number and p=10^m-3 is prime then 2*p is in the sequence.
`

`%C If m is a natural number and p=(10^m-7)/3 is prime then 4*p is in the sequence.
`

`%C a(14) > 3*10^12. - _Giovanni Resta_, Mar 21 2014
`

`%e sigma(14)-14 = 1+2+7 = 10, sigma(124)-124 = 1+2+4+31+62 = 100.
`

`%t r[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Do[If[!PrimeQ[n]&& r[DivisorSigma[1,n]-n]==1, Print[n]],{n, 200000000}]
`

`%Y Cf. A000203, A004086.
`

`%K nonn,base,more
`

`%O 1,1
`

`%A _Farideh Firoozbakht_, Mar 17 2014
`

`%E a(13) from _Giovanni Resta_, Mar 21 2014
`