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URL: https://oeis.org/A067795

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A067795
Numbers k such that 2*k+1 is the next prime after sigma(k).
1
2, 6, 8, 14, 44, 128, 315, 2144, 32768, 55328384, 815634435
OFFSET
1,1
COMMENTS
a(12) > 3*10^10. - Donovan Johnson, May 16 2011
36674855139367904, 56238963399763208, 39614081257135124284027437056, and 2535301200456482446891450105856 are terms. - Alexander Violette, Sep 19 2025
PROG
(PARI) isok(k) = nextprime(sigma(k)+1) == 2*k+1; \\ Michel Marcus, Sep 19 2025
CROSSREFS
Cf. A000203 (sigma).
Sequence in context: A199697 A339976 A135619 * A212353 A029933 A228366
KEYWORD
nonn,more
AUTHOR
Benoit Cloitre, Feb 07 2002
EXTENSIONS
Added missing term 2 and a(10)-a(11) from Donovan Johnson, May 16 2011
STATUS
approved