A143260 -id:A143260 - cp's OEIS frontend

A054658 Primes beginning 1, 3, 7, 9 whose reversals are nonprimes.

19, 103, 109, 127, 137, 139, 163, 173, 193, 197, 307, 317, 331, 349, 367, 379, 397, 719, 773, 911, 947, 977, 997, 1013, 1019, 1039, 1049, 1051, 1063, 1087, 1093, 1117, 1123, 1129, 1163, 1171, 1187, 1277, 1289, 1291, 1297, 1303, 1307, 1319, 1327, 1361

Offset: 1

Enoch Haga, Apr 18 2000

Or, primes whose reversals are composites ending in 1,3,7,9. - Lekraj Beedassy, Aug 02 2008

A subsequence of A143260. - Lekraj Beedassy, Aug 02 2008

			a(1)=19 because its reverse is a nonprime, 91.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A143260, A076056, A082768.

pbQ[p_]:=MemberQ[{1,3,7,9},IntegerDigits[p][[1]]]&&CompositeQ[IntegerReverse[p]]; Select[Prime[Range[300]],pbQ] (* Harvey P. Dale, Dec 02 2024 *)

Edited by N. J. A. Sloane, Aug 29 2008 at the suggestion of R. J. Mathar

A345389 Primes that are not emirps but whose digit reversal is a power of an emirp.

Original entry on oeis.org

9049, 9631, 125329, 148249, 180289, 1000651, 1027591, 1250023, 1460479, 1674931, 1825891, 1889221, 3989683, 9003703, 9041143, 9049231, 10612219, 14499601, 14663479, 16333459, 18005983, 18428101, 90876631, 98087809, 98873821, 100720513, 100922011, 101274443, 108344311, 121623511, 123736969

Offset: 1

J. M. Bergot and Robert Israel, Jun 17 2021

			a(3) = 125329 is a term because it is prime and its reversal 923521 = 31^4 where 31 is an emirp.

Cf. A006567, A143260.

revdigs:= proc(n) local L,i; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc:
isemirp:= proc(n) local r; if not isprime(n) then return false fi;
r:= revdigs(n); r <> n and isprime(r) end proc:
E:= select(isemirp, [seq(i,i=11..10^5,2)]):
EP:= map(proc(x) local i; seq(x^i,i=2..floor(log[x](10^10))) end proc,E):
EPR:= map(revdigs,EP):
sort(select(isprime,EPR));

cp's OEIS Frontend

A054658 Primes beginning 1, 3, 7, 9 whose reversals are nonprimes.

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