A076613 Palindromic primes with nonprime middle digit.

101, 181, 191, 313, 383, 787, 797, 919, 10601, 11411, 12421, 12821, 13831, 13931, 15451, 16061, 16661, 17471, 17971, 18181, 18481, 19891, 19991, 30103, 30403, 30803, 31013, 32423, 34843, 35053, 35153, 38083, 38183, 70607, 71917, 73037

Offset: 1

Author

Jani Melik, Oct 21 2002

Keywords

• easy
• nonn
• base

Examples

			a(12)=12821 is palindromic prime and its middle digit 8 is not prime, a(13)=13831 is palindromic prime and its middle digit 8 is not prime, a(14)=13931 is palindromic prime and its middle digit 9 is not prime, ...
		

Crossrefs

Cf. A002385, A069217.

Programs

Maple

ts_num_midpal := proc(n) local ad,adr,midigit; ad := convert(n,base,10): adr := ListTools[Reverse](ad): if nops(ad) mod 2 = 0 then return 1; fi; midigit := op( (nops(ad)+1)/2,ad ): if (isprime( midigit )='false' and adr=ad) then return 0; else return 1; fi end: ts_pra_n_pal := proc(n) local p1; p1 := ithprime(n): if ts_num_midpal(p1) = 0 then return (p1) fi end: apranpal := [seq(ts_pra_n_pal(i), i=1..100000)]: apranpal;