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 A246914 Primes p such that sigma(2p+1) = 3*(p+1). 6
 7, 103, 1487, 9679, 73727, 603679 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes p such that sigma(p+sigma(p)) = 3*sigma(p). Subsequence of A246910. The next term, if it exists, must be greater than 10^9. Conjecture: Also primes p such that sigma(2p+1) mod p = 3. - Jaroslav Krizek, Sep 28 2014 No other terms up to 10^11. - Michel Marcus, Feb 21 2020 LINKS Table of n, a(n) for n=1..6. EXAMPLE Prime 7 is in sequence because sigma(2*7 + 1) = sigma(15) = 24 = 3*(7+1). MAPLE with(numtheory): A246914:=n->`if`(isprime(n) and sigma(2*n+1) = 3*(n+1), n, NULL): seq(A246914(n), n=1..10^5); # Wesley Ivan Hurt, Oct 01 2014 MATHEMATICA Select[Prime[Range[1500]], DivisorSigma[1, 2# + 1] == 3# + 3 &] (* Alonso del Arte, Sep 07 2014 *) PROG (Magma) [n:n in[1..10^7] | SumOfDivisors(n+SumOfDivisors(n))eq 3*SumOfDivisors(n) and IsPrime(n)] (PARI) for(n=1, 10^6, p=prime(n); if(sigma(p+sigma(p))==3*sigma(p), print1(p, ", "))) \\ Derek Orr, Sep 07 2014 (PARI) forprime(p=2, 10^7, if(sigma(2*p+1)==3*(p+1), print1(p, ", "))) \\ Edward Jiang, Sep 07 2014 CROSSREFS Cf. A000203, A246456, A246910. Sequence in context: A142400 A032460 A267234 * A274670 A188946 A368440 Adjacent sequences: A246911 A246912 A246913 * A246915 A246916 A246917 KEYWORD nonn,more AUTHOR Jaroslav Krizek, Sep 07 2014 STATUS approved

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Last modified June 12 15:38 EDT 2024. Contains 373331 sequences. (Running on oeis4.)