The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A173071 Palindromic mountain primes. 3
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms have an odd number of digits. - Emeric Deutsch, Mar 09 2010 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..39 EXAMPLE a(6) = 12721; is a palindromic mountain prime. . . . . . . . . . . . . 7 . . . . . . . . . . . . . . . . . . . . . . . 2 . 2 . 1 . . . 1 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 PROG (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 CROSSREFS Cf. A002113, A002385, A134810, A134811, A134941, A134951. Sequence in context: A167845 A273049 A134951 * A164294 A155924 A270237 Adjacent sequences:  A173068 A173069 A173070 * A173072 A173073 A173074 KEYWORD nonn,base,fini,full AUTHOR Omar E. Pol, Feb 09 2010 EXTENSIONS More terms from Emeric Deutsch, Mar 09 2010, corrected Mar 19 2010 a(22)-a(27) from Donovan Johnson, Jul 22 2010 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 19 08:05 EDT 2021. Contains 347556 sequences. (Running on oeis4.)