

A078496


Smallest prime p such that p>n and 2*np is also prime.


12



5, 7, 7, 11, 11, 11, 13, 17, 13, 19, 17, 17, 19, 23, 19, 31, 23, 23, 31, 29, 29, 31, 29, 31, 37, 41, 31, 43, 41, 37, 37, 41, 41, 43, 47, 41, 43, 53, 43, 67, 47, 47, 61, 53, 53, 61, 53, 59, 61, 59, 61, 67, 59, 61, 73, 71, 61, 79, 71, 67, 67, 71, 71, 73, 83, 71, 73, 83, 73, 79
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OFFSET

4,1


COMMENTS

Suggested by Goldbach Conjecture.
Values of q from A143697. This follows from the factorization n^2k^2 = (nk)(n+k).


LINKS



FORMULA

n>3 integer; a(n)=min{p: p>n; p, 2*np are primes}.


EXAMPLE

a(11)=17.


MATHEMATICA

Table[p=n+1; q=2np; While[q>0&&!(PrimeQ[p]&&PrimeQ[q]), p++; q ]; p, {n, 4, 100}]


PROG

(PARI) a(n) = {my(p=nextprime(n+1)); while(!isprime(2*np), p = nextprime(p+1)); p; } \\ Michel Marcus, Oct 22 2016


CROSSREFS



KEYWORD

nonn


AUTHOR

Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), Nov 26 2002


EXTENSIONS



STATUS

approved



