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 A235710 Composite numbers n such that sum of the proper divisors of n is a power of 10. 0
 14, 124, 194, 1324, 1994, 13324, 133324, 1130324, 1333324, 13333324, 62496048, 133333324, 92782317392 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified September 14 01:28 EDT 2024. Contains 375910 sequences. (Running on oeis4.)