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A072687 Number of primes with prime length names in range 1 -> 10^n. 2
3, 8, 39, 269, 3047, 14288, 140205, 1567591, 10764655 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence uses "and" (e.g., "one hundred and one") and does not count spaces, commas, or hyphens. - Michael S. Branicky, Mar 08 2021

LINKS

Table of n, a(n) for n=1..9.

Sean A. Irvine, Java program (github)

EXAMPLE

E.g., from the sequence of the valid primes (A072686) there are three prime-length primes between 1 and 10: 2,3,7; therefore a(1)=3.

23 ("twentythree", 11 letters) and 109 ("one hundred and nine", 17 letters) are counted.

PROG

(Python)

from num2words import num2words

from sympy import isprime, primerange

def n2w(n):

  return num2words(n).replace(", ", "").replace(" ", "").replace("-", "")

def a(n): return sum(isprime(len(n2w(p))) for p in primerange(2, 10**n))

print([a(n) for n in range(1, 7)]) # Michael S. Branicky, Mar 08 2021

CROSSREFS

Cf. A072686.

Sequence in context: A180368 A108262 A034892 * A260817 A262126 A110561

Adjacent sequences:  A072684 A072685 A072686 * A072688 A072689 A072690

KEYWORD

more,nonn,word

AUTHOR

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 02 2002

EXTENSIONS

a(6)-a(8) from Sean A. Irvine, Nov 08 2011

a(8) corrected by Sean A. Irvine, Apr 28 2019

a(8) corrected and a(9) from Michael S. Branicky, Mar 08 2021

STATUS

approved

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Last modified January 27 15:07 EST 2022. Contains 350607 sequences. (Running on oeis4.)