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A113838 Palindromes sandwiched between twin primes. 1
4, 6, 282, 828, 858, 2112, 21012, 21612, 23832, 26262, 26862, 28182, 80208, 81018, 82728, 84348, 89598, 89898, 240042, 246642, 270072, 276672, 2035302, 2109012, 2136312, 2155512, 2182812, 2422242, 2428242, 2460642, 2499942, 2529252 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n > 2, the first and last digit of a(n) are either 2 or 8. - Chai Wah Wu, Jan 06 2016

Intersection of A002113 and A014574. - Michel Marcus, Jan 08 2016

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..10000

EXAMPLE

282 is a palindrome and 281 and 283 are twin primes.

MATHEMATICA

palQ[n_]:= n == FromDigits@Reverse@IntegerDigits@n; lst={}; Do[If[palQ[n] && PrimeQ[n-1] && PrimeQ[n+1], AppendTo[lst, n]], {n, 2, 10^7, 2}]; lst

palQ[n_]:=Module[{idn=IntegerDigits[n]}, idn==Reverse[idn]]; Mean[#]&/@ Select[ Select[ Partition[Prime[Range[190000]], 2, 1], Last[#]-First[#] == 2&], palQ[Mean[#]]&] (* Harvey P. Dale, Jan 18 2012 *)

PROG

(PARI) isok(n) = my(d = digits(n)); (Vecrev(d)==d) && isprime(n-1) && isprime(n+1); \\ Michel Marcus, Jan 08 2016

CROSSREFS

Cf. A002113 (palindrome), A014574 (average of twin prime pair).

Sequence in context: A081970 A076098 A141568 * A056831 A027717 A035481

Adjacent sequences:  A113835 A113836 A113837 * A113839 A113840 A113841

KEYWORD

base,nonn

AUTHOR

Giovanni Resta, Jan 24 2006

STATUS

approved

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Last modified September 18 07:50 EDT 2019. Contains 327168 sequences. (Running on oeis4.)