A227271 Numbers k such that k^3 + 2 is an emirp.

69, 105, 263, 311, 341, 425, 491, 515, 561, 575, 725, 993, 1091, 1133, 1193, 1521, 1583, 1991, 2085, 2153, 2289, 2351, 2379, 2415, 2433, 2441, 2543, 2601, 3203, 3225, 3285, 4245, 4263, 4541, 4713, 4955, 5039, 5073, 5463, 5499, 5523, 5651, 5675, 6779, 7295

Offset

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..1101

Example

a(1)=69: 69^3 + 2 = 328511; reversing its digits gives 115823, which is distinct from 328511, and both are primes, so 328511 is an emirp.

Maple

with(StringTools):K := proc(n) local a, b; a :=(n^3+2): b:=parse(Reverse(convert((a), string))):if (isprime(a)and isprime(b) and a<>b) then RETURN (n) fi: end: seq(K(n), n=1..100000); # K. D. Bajpai, Jul 04 2013
with(StringTools):K:=proc()local n, a, b, c;  c:=1; for n from 1 to 500000 do; a:= (n^3+2); b:=parse(Reverse(convert((a), string))); if isprime(a)and isprime(b)and a<>b  then lprint(c, n);  c:=c+1; fi;  od; end: K(); # K. D. Bajpai, Jul 04 2013

Mathematica

emirpQ[n_]:=Module[{idn=IntegerDigits[n^3+2], rev}, rev=Reverse[idn]; idn != rev && And@@PrimeQ[FromDigits/@{idn, rev}]]; Select[Range[7500], emirpQ] (* Harvey P. Dale, Jul 04 2013 *)

Crossrefs

Cf. A006567 (Emirps, primes whose reversal is a different prime).

Sequence in context: A044037 A287092 A111065 * A004237 A004238 A039541

Adjacent sequences: A227268 A227269 A227270 * A227272 A227273 A227274

Keyword

nonn,base

Author

K. D. Bajpai, Jul 04 2013

Status

approved