A235710 Composite numbers n such that sum of the proper divisors of n is a power of 10.

14, 124, 194, 1324, 1994, 13324, 133324, 1130324, 1333324, 13333324, 62496048, 133333324, 92782317392

Offset

1,1

Comments

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

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

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

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

a(14) > 3*10^12. - Giovanni Resta, Mar 21 2014

Links

Table of n, a(n) for n=1..13.

Example

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

Mathematica

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

Crossrefs

Cf. A000203, A004086.

Sequence in context: A163942 A206628 A370966 * A239544 A167567 A188411

Adjacent sequences: A235707 A235708 A235709 * A235711 A235712 A235713

Keyword

nonn,base,more

Author

Farideh Firoozbakht, Mar 17 2014

Extensions

a(13) from Giovanni Resta, Mar 21 2014

Status

approved