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 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 Daniel Starodubtsev, Table of n, a(n) for n = 1..10000 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 Cf. A023242, A023272, A176223. Sequence in context: A106021 A032605 A099243 * A158721 A118501 A023244 Adjacent sequences: A176244 A176245 A176246 * A176248 A176249 A176250 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

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