

A103534


Concatenations of pairs of primes that differ by 1000.


3



131013, 191019, 311031, 611061, 971097, 1031103, 1091109, 1511151, 1631163, 1811181, 1931193, 2231223, 2291229, 2771277, 2831283, 3071307, 3671367, 3731373, 4091409, 4331433, 4391439, 4871487, 4991499, 5231523, 5711571
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OFFSET

1,1


COMMENTS

Integers in this sequence can never be prime, as they are all multiples of 3. They can be semiprimes, as with the values for which the smaller prime P is prime(i) for i = 25, 36, 63, 93, 127...


LINKS

Table of n, a(n) for n=1..25.


FORMULA

a(n) = Concatenate(P, P+1000) iff P prime and P+1000 prime.


EXAMPLE

1811181 is in this sequence because 181 is prime, 181+1000 = 1181 is prime and those two primes are concatenated. The result is not itself a prime, as 1811181 = 3 x 23 x 26249. But it does happen to read the same backwards (palindromatic) and upsidedown.


MATHEMATICA

10001#+1000&/@Select[Prime[Range[150]], PrimeQ[#+1000]&] (* Harvey P. Dale, Sep 01 2017 *)


CROSSREFS

Cf. A000040, A001358, A023201, A100750, A103195, A103206, A104718, A104719, A103523.
Sequence in context: A202935 A013893 A013693 * A239610 A165478 A051331
Adjacent sequences: A103531 A103532 A103533 * A103535 A103536 A103537


KEYWORD

base,easy,nonn


AUTHOR

Jonathan Vos Post, Mar 22 2005


STATUS

approved



