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A068368 Composite n such that sigma(2n+1)-sigma(n)=n+1. 0
16, 335, 8399, 12599, 16383, 62999, 546359, 743999, 2815199, 3046655, 3592655, 8422679, 25357439, 26356199, 29318279, 75428999, 112039199, 202417343, 226325999, 329611559, 335894159, 452921039 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes satisfying sigma(2p+1)-sigma(p)=p+1 are Sophie Germain primes A005384(n)

LINKS

Table of n, a(n) for n=1..22.

PROG

(PARI) for(n=1, 500000000, if((sigma(2*n+1)-sigma(n)==n+1) && (!isprime(n)), print1(n, ", ")))

CROSSREFS

Sequence in context: A223394 A218476 A240344 * A013993 A058722 A173906

Adjacent sequences:  A068365 A068366 A068367 * A068369 A068370 A068371

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Feb 28 2002

EXTENSIONS

More terms from Rick L. Shepherd, May 08 2002

STATUS

approved

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Last modified April 17 12:15 EDT 2014. Contains 240635 sequences.