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A262463
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If n is prime a(n) = n else a(n) = nextprime(reverse(n)), where "next prime" is the smallest prime >= n, see A007918.
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1
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2, 2, 3, 5, 5, 7, 7, 11, 11, 2, 11, 23, 13, 41, 53, 61, 17, 83, 19, 2, 13, 23, 23, 43, 53, 67, 73, 83, 29, 3, 31, 23, 37, 43, 53, 67, 37, 83, 97, 5, 41, 29, 43, 47, 59, 67, 47, 89, 97, 5, 17, 29, 53, 47, 59, 67, 79, 89, 59, 7, 61, 29, 37, 47, 59, 67, 67, 89, 97, 7, 71, 29, 73, 47, 59, 67, 79, 89, 79, 11, 19, 29
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n)=n if n is prime;
else b=reverse(n);
if b is prime a(n)=b else a(n)=nextprime(b);
(using "next prime" function as "smallest prime >= n"; see A007918. )
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EXAMPLE
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For n=7 a(7)=7.
For n=12, reverse(12)=21; a(12)=nextprime(21)=23.
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MATHEMATICA
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Table[Which[PrimeQ[n], n, PrimeQ[IntegerReverse[n]], IntegerReverse[n], True, NextPrime[ IntegerReverse[ n]]], {n, 100}] (* Harvey P. Dale, May 12 2018 *)
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PROG
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(PARI) rev(n)={d=digits(n); p=""; for(i=1, #d, p=concat(Str(d[i]), p)); return(eval(p))}
i=0; t=vector(200);
findn(n)={if(isprime(n), t[i++]=n, a=rev(n); b=nextprime(a); t[i++]=b); }
for(n=1, 200, findn(n)); t
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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