A098922 - OEIS

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

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..41.

EXAMPLE

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

MAPLE

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);

CROSSREFS

Cf. A004087, A095180.

Sequence in context: A119834 A095180 A101989 * A265324 A004087 A118495

Adjacent sequences: A098919 A098920 A098921 * A098923 A098924 A098925

KEYWORD

base,easy,nonn

AUTHOR

Jani Melik, Oct 18 2004

STATUS

approved