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A223609 Numbers n whose abundance is 10. Sigma(n)-2*n = 10. 5
40, 1696, 518656, 34358296576 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Suggested by N. J. A. Sloane and Robert G. Wilson v.

a(5) > 10^12.

a(5) > 10^13. - Giovanni Resta, Mar 29 2013

a(5) > 10^18. - Hiroaki Yamanouchi, Aug 23 2018

Any term x of this sequence can be combined with any term y of A101223 to satisfy the property (sigma(x)+sigma(y))/(x+y) = 2, which is a necessary (but not sufficient) condition for two numbers to be amicable. - Timothy L. Tiffin, Sep 13 2016

LINKS

Table of n, a(n) for n=1..4.

EXAMPLE

n = 34358296576. sigma(n)-2*n = 10.

MATHEMATICA

Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == 10 &]  (* Vincenzo Librandi, Sep 15 2016 *)

PROG

(PARI) for(n=1, 10^8, if(sigma(n)-2*n==10, print1(n ", ")))

(MAGMA) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq 10]; // Vincenzo Librandi, Sep 15 2016

CROSSREFS

Cf. A000203, A033880, A101223 (deficiency 10).

Sequence in context: A278431 A229584 A140702 * A145294 A147520 A190926

Adjacent sequences:  A223606 A223607 A223608 * A223610 A223611 A223612

KEYWORD

nonn,more

AUTHOR

Donovan Johnson, Mar 23 2013

STATUS

approved

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Last modified January 26 16:58 EST 2020. Contains 331280 sequences. (Running on oeis4.)