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A135242 Numbers n such that sigma(n) = 2*(n-reversal(n)). 1
10, 51, 430, 591, 922, 5991, 8350, 20210, 28810, 59211, 59991, 6673581, 8179030, 20158910, 203887910, 833549650, 2263048910, 2814442310, 7823347543, 78551146723, 81896108650, 281444442310, 770920338133, 832428872110, 7670112536751 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
If n=6*10^m-9 is semiprime then n is in the sequence (the proof is easy).
a(26) > 10^13. - Giovanni Resta, Jul 13 2015
LINKS
EXAMPLE
sigma(51)=72=2*(51-15)=2*(51-reversal(51)), so 51 is in the sequence.
MATHEMATICA
Do[If[2(n-FromDigits@Reverse@IntegerDigits@n)==DivisorSigma[1, n], Print[n]], {n, 70000000}]
CROSSREFS
Sequence in context: A030183 A224327 A219573 * A362673 A041186 A058827
KEYWORD
base,more,nonn
AUTHOR
Farideh Firoozbakht, Jan 04 2008
EXTENSIONS
a(15)-a(21) from Donovan Johnson, Dec 21 2008
a(22)-a(25) from Giovanni Resta, Jul 13 2015
STATUS
approved

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Last modified July 13 17:55 EDT 2024. Contains 374285 sequences. (Running on oeis4.)