A052024 - OEIS

A052024

Every suffix of palindromic prime a(n) is prime (left-truncatable).

2, 3, 5, 7, 313, 353, 373, 383, 797, 30103, 31013, 70607, 73037, 76367, 79397, 3002003, 7096907, 7693967, 700090007, 799636997, 70060906007, 3000002000003, 7030000000307, 300000020000003, 300001030100003, 310000060000013, 38000000000000000000083, 30000000004000300040000000003, 3000001000000000000000000000001000003

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..29.

I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265-267, 1977.

C. K. Caldwell, Left and Right truncatable primes.

Eric Weisstein's World of Mathematics, Prime strings

Index entries for sequences related to truncatable primes

MATHEMATICA

d[n_]:=IntegerDigits[n]; ltrQ[n_]:=And@@PrimeQ[NestWhileList[FromDigits[Drop[d[#], 1]]&, n, #>9&]]; palQ[n_]:=Reverse[x=d[n]]==x; Select[Prime[Range[550000]], palQ[#]&&ltrQ[#]&] (* Jayanta Basu, Jun 02 2013 *)

PROG

(Python)

from sympy import isprime

from itertools import count, islice

def agen(verbose=False):

prime_strings, alst = {"3", "7"}, []

yield from [2, 3, 5, 7]

for digs in count(2):

new_prime_strings = set()

for p in prime_strings:

for d in "123456789":

ts = d + "0"*(digs-1-len(p)) + p

if isprime(int(ts)):

new_prime_strings.add(ts)

prime_strings |= new_prime_strings

pals = [int(s) for s in new_prime_strings if s == s[::-1]]

yield from sorted(pals)

if verbose: print("...", digs, len(prime_strings), time()-time0)

print(list(islice(agen(), 20))) # Michael S. Branicky, Apr 04 2022

CROSSREFS

Cf. A002385, A033664, A024785, A032437, A020994, A024770, A052023, A052025, A050986, A050987.

Sequence in context: A090719 A088297 A180015 * A052023 A052025 A359491

Adjacent sequences: A052021 A052022 A052023 * A052025 A052026 A052027

KEYWORD

nonn,base

AUTHOR

G. L. Honaker, Jr. and Patrick De Geest, Nov 15 1999

EXTENSIONS

Inserted missing 31013 by Jayanta Basu, Jun 02 2013

a(27)-a(29) from Michael S. Branicky, Apr 04 2022

STATUS

approved