A173071 Palindromic mountain primes.
131, 151, 181, 191, 12421, 12721, 12821, 13831, 13931, 14741, 17971, 1235321, 1245421, 1257521, 1268621, 1278721, 1456541, 1469641, 1489841, 1579751, 1589851, 123484321, 123494321, 123575321, 136797631, 167898761, 12345854321
Offset: 1
Examples
a(6) = 12721; is a palindromic mountain prime. . . . . . . . . . . . . 7 . . . . . . . . . . . . . . . . . . . . . . . 2 . 2 . 1 . . . 1
Links
- Chai Wah Wu, Table of n, a(n) for n = 1..39
Programs
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Maple
a := proc (n) local rev, n1: rev := proc (n) local nn: nn := convert(n, base, 10): add(nn[j]*10^(nops(nn)-j), j = 1 .. nops(nn)) end proc: n1 := convert(n, base, 10): if n1[1]=1 and isprime(n) = true and rev(n) = n and n1[1] < n1[2] and n1[2] < n1[3] and n1[3] < n1[4] then n else end if end proc: seq(a(n), n = 1000000 .. 9999999); # this program works only for 7-digit numbers; easily adjustable for other (2k+1)-digit numbers # Emeric Deutsch, Mar 09 2010
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Python
from itertools import combinations from gmpy2 import is_prime A173071_list = [] for l in range(1,10): for i in combinations('23456789',l): s = '1'+''.join(i) p = int(s+s[l-1::-1]) if is_prime(p): A173071_list.append(p) # Chai Wah Wu, Nov 05 2015
Extensions
More terms from Emeric Deutsch, Mar 09 2010, corrected Mar 19 2010
a(22)-a(27) from Donovan Johnson, Jul 22 2010
Comments