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A322947
Numbers k such that 2k + 1 is a palindromic prime.
1
1, 2, 3, 5, 50, 65, 75, 90, 95, 156, 176, 186, 191, 363, 378, 393, 398, 459, 464, 5150, 5250, 5300, 5655, 5705, 6210, 6360, 6410, 6665, 6915, 6965, 7170, 7370, 7725, 7775, 8030, 8180, 8280, 8330, 8735, 8985, 9090, 9240, 9695, 9945, 9995, 15051, 15101, 15201, 15351, 15401, 15506, 15756
OFFSET
1,2
LINKS
FORMULA
a(n) = (A002385(n+1) - 1)/2. - Rémy Sigrist, Jan 01 2019
EXAMPLE
5 is in the sequence, because 2 * 5 + 1 = 11 is a prime palindrome.
MATHEMATICA
Select[Range[16000], And[PrimeQ@ #, PalindromeQ@ #] &[2 # + 1] &] (* Michael De Vlieger, Jan 01 2019 *)
PROG
(PARI) isok(n) = my(p=2*n+1, d=digits(p)); isprime(p) && (Vecrev(d) == d); \\ Michel Marcus, Jan 01 2019
CROSSREFS
Cf. A002385 (palindromic primes).
Sequence in context: A060380 A062608 A041791 * A056720 A100850 A309607
KEYWORD
nonn,base
AUTHOR
Daniel Starodubtsev, Dec 31 2018
STATUS
approved