A244190 a(n) = most common 2-digit ending for a prime with n digits, or 0 if there is a tie.

0, 57, 0, 97, 71, 93, 59, 73, 47, 51, 19, 27

Offset

2,2

Comments

21 and 23 are tied with 4-digit primes so a(4) = 0.

Links

Table of n, a(n) for n=2..13.

Example

Of the primes with 3 digits, the most common 2 digit ending is 57. Thus a(3) = 57.

Prog

(Python)
import sympy
from sympy import isprime
def end(d, n):
  lst = []
  for k in range(10**(d-1), 10**d):
    num = ''
    count = 0
    for i in range(10**(n-d-1), 10**(n-d)):
      if isprime(int(str(i)+str(k))):
        count += 1
    lst.append(count)
  a = max(lst)
  lst[lst.index(a)] = 0
  b = max(lst)
  if a == b:
    return 0
  else:
    return max(a, b) + 10**(d-1)
n = 3
while n < 10:
  print(end(2, n), end=', ')
  n += 1

Crossrefs

Cf. A244189.

Sequence in context: A101355 A285179 A307938 * A013682 A278068 A126828

Adjacent sequences: A244187 A244188 A244189 * A244191 A244192 A244193

Keyword

nonn,base,hard,more

Author

Derek Orr, Jun 22 2014

Extensions

a(9) from Tom Edgar, Jun 24 2014

a(10)-a(12) from Hiroaki Yamanouchi, Jul 11 2014

a(13) from Marek Hubal, Mar 04 2019

Status

approved