A130112 Primes prime(n) such that 10*prime(n)+prime(n+2) is not prime.

2, 19, 23, 29, 31, 37, 43, 47, 53, 59, 61, 71, 73, 79, 83, 97, 103, 107, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 191, 197, 211, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 293, 307, 311, 317, 331, 349, 353, 359, 373, 379, 383, 389

Offset

1,1

Links

Table of n, a(n) for n=1..56.

Example

a(7)=43 because 10*41+53=483 and 483=3*7*23 is not prime,
a(8)=47 because 10*47+59=529 and 529=23^2 is not prime,
a(9)=53 because 10*53+61=591 and 591=3*197 is not prime, ...

Maple

ts_p6_02:=proc(n) local a, b, i, ans; ans := [ ]: for i from 1 to n do a := 10*ithprime(i)+ithprime(i+2): if (isprime(a)=false) then ans := [ op(ans), ithprime(i) ]: fi od; RETURN(ans) end: ts_p6_02(300);

Mathematica

Transpose[Select[Partition[Prime[Range[200]], 3, 1], !PrimeQ[10First[#]+ Last[#]]&]][[1]] (* Harvey P. Dale, Jan 04 2012 *)

Crossrefs

Cf. A129900.

Sequence in context: A042247 A041451 A268492 * A019348 A155025 A191068

Adjacent sequences: A130109 A130110 A130111 * A130113 A130114 A130115

Keyword

nonn

Author

Jani Melik, Aug 01 2007

Status

approved