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

1,1

Links

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

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. )

Example

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

Mathematica

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

Prog

(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

Crossrefs

Cf. A000040, A077018.

Sequence in context: A090473 A380960 A113636 * A151800 A259430 A290838

Adjacent sequences: A262460 A262461 A262462 * A262464 A262465 A262466

Keyword

nonn,base

Author

Maghraoui Abdelkader, Sep 23 2015

Status

approved