|
%I #36 Mar 20 2015 19:13:17
%S 11,251,1429,906949,1050449,1058389,3728113,9665329,13623667,14320489,
%T 30668003,30910391,45717377,49437001,55544959,57510911,58206653,
%U 58772257,69490901,72191321,73625789,75235973,79396433,99673891,103821169,104662139,121322449,125938889,147210257,164810311,169844879,170650169,201991721
%N Primes p such that sopfr(p-1) = sopfr(p+1) is also prime, where sopfr is A001414.
%C The first three terms were computed by J. M. Bergot (personal communication from J. M. Bergot to _N. J. A. Sloane_, May 16 2011).
%C The number of terms < 10^n: 0, 1, 2, 3, 3, 4, 8, 24, 70, 253, 839, ..., . - _Robert G. Wilson v_, May 31 2011
%H Charles R Greathouse IV and Robert G. Wilson v, <a href="/A190680/b190680.txt">Table of n, a(n) for n = 1.. 2592</a> (Charles R Greathouse IV to 1536, Robert G. Wilson v to 2592)
%e sopfr(250) = sopfr(2*5^3) = 2 + 5*3 = 17 = 2*2 + 3*2 + 7 = sopfr(2^2*3^2*7) = sopfr(252), and 17 and 251 are prime, so 251 is in this sequence.
%t f[n_] := Plus @@ Flatten[ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@ n]; fQ[n_] := Block[{pn = f[n - 1], pp = f[n + 1]}, pn == pp && PrimeQ@ pn]; p = 2; lst = {}; While[p < 216000000, If[ fQ@ p, AppendTo[lst, p]]; p = NextPrime@ p]; lst (* _Robert G. Wilson v_, May 18 2011 *)
%Y Subsequence of A086711. Cf. A190722.
%K nonn
%O 1,1
%A _Charles R Greathouse IV_, May 16 2011
|
