A050987 Number of n-digit left-truncatable primes.

4, 11, 39, 99, 192, 326, 429, 521, 545, 517, 448, 354, 276, 212, 117, 72, 42, 24, 13, 6, 5, 4, 3, 1, 0

Offset

1,1

Comments

The sequence is well defined for any positive integer, with a(n) = 0 for n >= 25. But it makes sense to consider it to be full & finite. - M. F. Hasler, Nov 07 2018

Links

Table of n, a(n) for n=1..25.

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

P. De Geest, The list of 4260 left-truncatable primes

Eric Weisstein's World of Mathematics, Truncatable Prime.

Index entries for sequences related to numbers of primes in various ranges

Index entries for sequences related to truncatable primes

Prog

(PARI) A050987=vector(25, n, #p=concat(apply(p->select(isprime, vector(9, i, i*10^(n-1)+p)), if(n>1, p)))) \\ M. F. Hasler, Nov 07 2018
(Python)
from sympy import isprime
def alst():
  primes, alst = [2, 3, 5, 7], [4]
  while len(primes) > 0:
    candidates = set(int(d+str(p)) for p in primes for d in "123456789")
    primes = [c for c in candidates if isprime(c)]
    alst.append(len(primes))
  return alst
print(alst()) # Michael S. Branicky, Apr 11 2021

Crossrefs

Cf. A033664, A024785, A032437, A020994, A024770, A052023, A052024, A052025, A050986.

Sequence in context: A255706 A355888 A203161 * A137191 A106269 A126758

Adjacent sequences: A050984 A050985 A050986 * A050988 A050989 A050990

Keyword

base,nonn,easy,fini,full

Author

Eric W. Weisstein

Extensions

Edited by Ray Chandler, Mar 13 2007

a(25) = 0 added by M. F. Hasler, Nov 07 2018

Status

approved