A279213 Primes formed by concatenating n with n-3.
41, 107, 1613, 2017, 3229, 4441, 4643, 5653, 7673, 9491, 106103, 116113, 124121, 130127, 136133, 170167, 172169, 182179, 184181, 196193, 206203, 212209, 214211, 220217, 224221, 230227, 272269, 274271, 280277, 302299, 304301, 320317, 322319, 326323, 334331
Offset: 1
Examples
For n = 16, n-3 = 13. Concatenating 16 and 13 gives 1613 which is a prime. So, 1613 is in the sequence. - _Indranil Ghosh_, Jan 23 2017
Links
- Indranil Ghosh, Table of n, a(n) for n = 1..10000
Programs
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Magma
[m: n in [4..400 by 2] | IsPrime(m) where m is Seqint(Intseq(n-3) cat Intseq(n))];
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Mathematica
Select[Table[FromDigits[Join[Flatten[IntegerDigits[{n, n -3}]]]], {n, 400}], PrimeQ] -
PARI
terms(n) = my(i=0, k=3); while(i < n, my(x=eval(Str(k, k-3))); if(ispseudoprime(x), print1(x, ", "); i++); k++) /* Print initial 35 terms as follows: */ terms(35) \\ Felix Fröhlich, Jan 23 2017
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Python
from sympy import isprime i=4 j=1 while j<=10000: if isprime(int(str(i)+str(i-3)))==True: print(str(j)+" "+str(i)+str(i-3)) j+=1 i+=1 # Indranil Ghosh, Jan 23 2017