STATUS
proposed
approved
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Revision History for A076623
(Bold, blue-underlined text is an addition; faded, red-underlined text is aShowing entries 1-10 | older changes
STATUS
editing
proposed
COMMENTS
Approximation of a(b) by (PARI) code: l(b)=c=b*(b-1)/log(b)/eulerphi(b);\ return(floor((primepi(b)-omega(b))*exp(c)/c)); - _Robert Gerbicz_, Nov 02 2008
PROG
(PARI code from Robert Gerbicz, Oct 31 2008)
(PARI)
L=M; A=vector(L, i, B[i])); return(ct) \\ _Robert Gerbicz_, Oct 31 2008
KEYWORD
nonn,base,more,changed
EXTENSIONS
Correction of a(18) and approximation for a(n). - _corrected by _Robert Gerbicz_, Nov 02 2008
STATUS
proposed
editing
STATUS
editing
proposed
EXTENSIONS
a(24) - a(29) from Martin Fuller, Nov 24 2008
COMMENTS
a(24) = 1052029701 based on strong BPSW pseudoprimes. Other terms up to a(29) use proved primes. - Martin Fuller, Nov 24 2008
LINKS
I. O. Angell, I. O. and H. J. Godwin, H. J., <a href="http://dx.doi.org/10.1090/S0025-5718-1977-0427213-2">On Truncatable Primes</a>, Math. Comput. 31, 265-267, 1977.
Michael S. Branicky, <a href="/A076623/a076623.py.txt">String-based Python Program</a>
Michael S. Branicky, <a href="/A076623/a076623.py.txt">String-based Python Program</a>
LINKS
Michael S. Branicky, <a href="/A076623/a076623.py.txt">String-based Python Program</a>
PROG
(Python) # works for all n; link has faster string-based version for n < 37
from sympy import isprime, primerange
from sympy.ntheory.digits import digits
def fromdigits(digs, base):
return sum(d*base**i for i, d in enumerate(digs))
def a(n):
prime_lists, an = [(p, ) for p in primerange(1, n)], 0
while len(prime_lists) > 0:
an += len(prime_lists)
candidates = set(p+(d, ) for p in prime_lists for d in range(1, n))
prime_lists = [c for c in candidates if isprime(fromdigits(c, n))]
return an
print([a(n) for n in range(2, 12)]) # Michael S. Branicky, Apr 27 2022
STATUS
approved
editing
STATUS
editing
approved
COMMENTS
a(24)=1052029701 based on strong BPSW pseudoprimes. Other terms up to a(29) use proved primes. [From _- _Martin Fuller_, Nov 24 2008]
MAPLE
for b from 2 do print(b, A076623(b)) ; end do: # _R. J. Mathar, _, Jun 01 2011
STATUS
approved
editing
COMMENTS
a(24)=1052029701 based on strong BPSW pseudoprimes. Other terms up to a(29) use proved primes. [From _Martin Fuller (martin_n_fuller(AT)btinternet.com), _, Nov 24 2008]
EXTENSIONS
a(12) corrected from 170051 to 170053 by _Martin Fuller (martin_n_fuller(AT)btinternet.com), _, Oct 31 2008
a(24) - a(29) from _Martin Fuller (martin_n_fuller(AT)btinternet.com), _, Nov 24 2008