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A246858 Composite numbers n such that sigma(n+sigma(n)) = 2*sigma(n). 1
329, 413, 623, 869, 979, 1819, 2585, 3107, 3173, 3197, 3887, 4235, 4997, 5771, 6149, 6187, 6443, 7409, 8399, 8759, 14429, 15323, 18515, 19019, 21181, 21413, 23989, 26491, 29749, 30355, 31043, 32623, 34009, 34177, 39737, 47321, 47845, 51389, 53311, 56419 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Complement of A005384 (Sophie Germain primes) with respect to A246857.

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

Number 329 (with sigma(329) = 384) is in sequence because sigma(329+sigma(329)) = sigma(713) = 768 = 2*384.

PROG

(MAGMA) [n:n in[1..1000] | SumOfDivisors(n+SumOfDivisors(n)) eq 2*SumOfDivisors(n) and not IsPrime(n)]

(PARI) lista(nn) = {forcomposite(n=2, nn, if (sigma(n+sigma(n)) == 2*sigma(n), print1(n, ", ")); ); } \\ Michel Marcus, Sep 05 2014

CROSSREFS

Cf. A000040, A005384, A246857.

Sequence in context: A289340 A252004 A278352 * A253054 A273615 A231362

Adjacent sequences:  A246855 A246856 A246857 * A246859 A246860 A246861

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Sep 05 2014

STATUS

approved

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Last modified September 22 12:42 EDT 2019. Contains 327307 sequences. (Running on oeis4.)