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A227271 Numbers k such that k^3 + 2 is an emirp. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
KEYWORD
nonn,base
AUTHOR
K. D. Bajpai, Jul 04 2013
STATUS
approved

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Last modified February 26 21:28 EST 2024. Contains 370352 sequences. (Running on oeis4.)