login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A176247 Primes p which give a prime iterated by f(p) = 2*p + 13 for at least two steps. 2
2, 5, 17, 23, 47, 107, 113, 227, 233, 317, 353, 467, 743, 827, 1013, 1163, 1223, 1283, 1493, 1697, 1823, 1877, 2063, 2333, 2543, 2957, 3323, 3467, 3767, 3797, 4013, 4397, 4523, 5297, 5393, 5507, 5693, 5717, 5897, 5927, 6053, 6317, 6473, 6737, 6947, 6977 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Subsequence of A176223.
p, f(p) = 2*p + 13, q = f(f(p)) = 4*p + 39 to be primes.
Necessarily for such primes p > 5, the LSD (least significant digit) is either 3 or 7, since an LSD of 1 gives the LSD of f(p) equal to 5 and an LSD of 9 gives the LSD of f(f(p)) equal to 5.
LINKS
EXAMPLE
f(2) = 17 = prime(7), f(17) = 47 = prime(15), 2 is first term.
f(5) = 23 = prime(9), f(23) = 59 = prime(17), 5 is 2nd term.
Note first resulting palindromic prime: f(3323) = 6659 = prime(858), q = 13331 = prime(1583) = palprime(29).
MATHEMATICA
Select[Prime@ Range[10^3], AllTrue[NestList[2 # + 13 &, #, 2], PrimeQ] &] (* Michael De Vlieger, Mar 14 2020 *)
PROG
(PARI) isok(n) = isprime(n) && isprime(p=2*n+13) && isprime(2*p+13) \\ Michel Marcus, Jun 28 2013
CROSSREFS
Sequence in context: A106021 A032605 A099243 * A158721 A118501 A023244
KEYWORD
nonn
AUTHOR
Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Apr 13 2010
EXTENSIONS
More terms from Michel Marcus, Jun 28 2013
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 3 15:08 EST 2024. Contains 370512 sequences. (Running on oeis4.)