A095180 -id:A095180 - cp's OEIS frontend

A098922 Reverse digits of largest primes, append to sequence if result is larger prime then previous one with reverse digits.

2, 3, 5, 7, 11, 31, 71, 73, 97, 101, 701, 941, 971, 991, 9001, 9601, 9721, 9931, 9941, 9967, 70001, 90001, 93001, 96001, 97001, 99401, 99611, 99721, 99881, 99923, 99989, 940001, 972001, 973001, 996001, 997001, 999101, 999331, 999431, 999631, 999931

Offset: 1

Jani Melik, Oct 18 2004

			The prime 37 in reverse is 73. 73 is prime and is larger than previous prime (17), written with reverse digits 71.

Cf. A004087, A095180.

obrni_stev:=proc(n) local i, tren, tren1, st, ans; ans:=[ ]: tren:=n: tren1:=0: for i while (tren>0) do st:=round( 10*frac(tren/10) ): ans:=[ op(ans), st ]: tren:=trunc(tren/10): od; for i from 0 to nops(ans)-1 do tren1:= tren1 + op(nops(ans)-i, ans)*10^(i); od: RETURN(tren1); end: ts_inv_prav_pra:= proc(n) local i, tren, ans; tren:=0: ans:=[ ]: for i from 1 to n do if ( isprime( i ) = 'true' and isprime( obrni_stev (i) )='true' and obrni_stev(i) > tren ) then ans:=[ op(ans),obrni_stev(i) ]; tren:=obrni_stev(i); fi: od: RETURN(ans); end: ts_inv_prav_pra(200000);

A321523 List of pairs: primes whose reversal is also prime, each followed by its reversal.

Original entry on oeis.org

2, 2, 3, 3, 5, 5, 7, 7, 11, 11, 13, 31, 17, 71, 31, 13, 37, 73, 71, 17, 73, 37, 79, 97, 97, 79, 101, 101, 107, 701, 113, 311, 131, 131, 149, 941, 151, 151, 157, 751, 167, 761, 179, 971, 181, 181, 191, 191, 199, 991, 311, 113, 313, 313, 337, 733, 347, 743, 353, 353

Offset: 1

Kritsada Moomuang, Nov 12 2018

			The sequence begins:
     2,  2;
     3,  3;
     5,  5;
     7,  7;
    11, 11;
    13, 31;
    17, 71;
    31, 13;
    37, 73;
    71, 17;
...
107 has its reversal as 701.
971 has its reversal as 179.

Subsequence of A135020.

Cf. A000040, A004086, A007500, A095180, A180022.

Flatten@ Table[ If[PrimeQ[r = IntegerReverse@ p], {p,r}, {}], {p, Prime@ Range@ 71}] (* Giovanni Resta, Nov 13 2018 *)

forprime(p=1, 353, r=fromdigits(Vecrev(digits(p))); if (isprime(r), print1(p ", " r ", "))) \\ Rémy Sigrist, Nov 16 2018

a(2n-1) = A007500(n).
a(2n) = A004086(A007500(n)).
a(2n) = A095180(n). - Rémy Sigrist, Nov 16 2018

cp's OEIS Frontend

A098922 Reverse digits of largest primes, append to sequence if result is larger prime then previous one with reverse digits.

Views

Author

Keywords

Examples

Crossrefs

Programs

Maple