A262463 If n is prime a(n) = n else a(n) = nextprime(reverse(n)), where "next prime" is the smallest prime >= n, see A007918.

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

Offset: 1

Author

Maghraoui Abdelkader, Sep 23 2015

Keywords

• nonn
• base

Examples

			For n=7 a(7)=7.
For n=12, reverse(12)=21; a(12)=nextprime(21)=23.
		

Links

• Maghraoui Abdelkader, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A000040, A077018.

Programs

Mathematica

Table[Which[PrimeQ[n],n,PrimeQ[IntegerReverse[n]],IntegerReverse[n], True, NextPrime[ IntegerReverse[ n]]],{n,100}] (* Harvey P. Dale, May 12 2018 *)

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

Formula

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. )