A070955 Numbers k such that k concatenated with k-1 0's and its reversal is prime.

1, 122, 346, 1454, 3526, 7408, 14690

Offset

1,2

Comments

a(2) and a(3) give certified primes with Primo. a(4) gives a probable prime.

a(7) > 10^4.

Links

Table of n, a(n) for n=1..7.

Example

122 is a term because 12200...(121 zeros)...000221 is prime.

Prog

(Python)
from sympy import isprime
def afind(limit, startat=1):
    for k in range(startat, limit+1):
        s = str(k)
        if isprime( int(s + "0"*(k-1) + s[::-1]) ): print(k, end=", ")
        k += 10**(len(s)-1) if s[0] in "24568" else 1
afind(1500) # Michael S. Branicky, Nov 30 2021

Crossrefs

Sequence in context: A369598 A276303 A224598 * A195856 A116216 A203805

Adjacent sequences: A070952 A070953 A070954 * A070956 A070957 A070958

Keyword

base,more,nonn

Author

Jason Earls, May 25 2002

Extensions

a(5), a(6) from Max Alekseyev, May 21 2011

a(7) from Michael S. Branicky, Nov 30 2021

Status

approved