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A171130
Primes p such that sum of divisors of p+2 is prime.
3
2, 7, 23, 727, 2399, 5039, 7919, 17159, 28559, 29927, 85847, 458327, 552047, 579119, 707279, 1190279, 3418799, 3728759, 4532639, 5166527, 5331479, 7447439, 10374839, 24137567, 25877567, 28398239, 30260999, 43546799, 47458319, 52258439, 56957207, 62425799
OFFSET
1,1
COMMENTS
If p is a term then p+2 is a prime power with an even exponent (A056798). - Amiram Eldar, Aug 01 2024
LINKS
EXAMPLE
2 is a term since it is a prime and sigma(2+2) = 7 is a prime.
7 is a term since it is a prime and sigma(7+2) = 13 is a prime.
23 is a term since it is a prime and sigma(23+2) = 31 is a prime.
727 is a term since it is a prime and sigma(727+2) = 1093 is a prime.
MAPLE
with(numtheory): A171130:=n->`if`(isprime(n) and isprime(sigma(n+2)), n, NULL): seq(A171130(n), n=1..10^5); # Wesley Ivan Hurt, Sep 30 2014
MATHEMATICA
f[n_]:=Plus@@Divisors[n]; lst={}; Do[p=Prime[n]; If[PrimeQ[f[p+2]], AppendTo[lst, p]], {n, 10!}]; lst
Select[Prime[Range[700000]], PrimeQ[DivisorSigma[1, #+2]]&] (* Harvey P. Dale, Jun 23 2011 *)
PROG
(PARI) lista(nn) = forprime(p=2, nn, if (isprime(sigma(p+2)), print1(p, ", "))); \\ Michel Marcus, Sep 30 2014
(PARI) lista(kmax) = {my(p); for(k = 1, kmax, if(isprime(k) || isprimepower(k), p = k^2-2; if(isprime(p) && isprime(sigma(p+2)), print1(p, ", ")))); } \\ Amiram Eldar, Aug 01 2024
CROSSREFS
Sequence in context: A139522 A163158 A355981 * A112089 A075062 A022497
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Michel Marcus, Sep 30 2014
STATUS
approved