A108184 a(n) = smallest prime such that a(n) + 2n is also prime and such that a(n) > a(n-1).
2, 3, 7, 11, 23, 31, 41, 47, 67, 71, 83, 109, 113, 131, 139, 149, 167, 193, 197, 233, 241, 251, 263, 271, 283, 317, 331, 347, 353, 373, 379, 401, 439, 443, 479, 487, 491, 503, 523, 541, 563, 571, 577, 587, 613, 619, 641, 727, 733, 761, 787, 809, 863, 877
Offset: 0
Examples
a(0)=2 since 2+0=2 is prime; a(1)=3 since 3+2=5 is prime. a(2)=7 since 7+4=11 is prime; 5 is not in the sequence since 5+4=9 is not prime.
Links
- T. D. Noe, Table of n, a(n) for n = 0..10000
Programs
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Maple
A108184 := proc(n) option remember; if n = 1 then 3; else for a from procname(n-1)+1 do if isprime(a) and isprime(a+2*n) then RETURN(a) ; fi; od: fi; end: seq(A108184(n),n=1..100) ; # R. J. Mathar, Jan 31 2009
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Mathematica
t = {2}; Do[p = NextPrime[t[[-1]]]; While[! PrimeQ[p + 2 n], p = NextPrime[p]]; AppendTo[t, p], {n, 100}]; t (* T. D. Noe, Feb 04 2014 *) -
PARI
A108184(maxp) = {my(a=[2], n=1); forprime(p=3, maxp, if(isprime(p+2*n), n++; a=concat(a, p))); a} \\ Colin Barker, Feb 03 2014
Extensions
Edited and extended by Ray Chandler, Jul 07 2005
Edited by N. J. A. Sloane, Feb 11 2009 at the suggestion of R. J. Mathar
Comments