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A032694 Exactly 4 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime. 1
11, 19, 27, 31, 41, 47, 53, 67, 73, 87, 91, 97, 109, 129, 151, 153, 187, 203, 209, 217, 231, 243, 273, 283, 311, 323, 373, 389, 423, 433, 447, 451, 467, 481, 539, 549, 581, 583, 591, 607, 621, 623, 637, 643, 657, 659, 663, 669, 673, 677, 691, 693, 699, 753 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

EXAMPLE

If a(n) = 109 then we find '1'109, '3'109, '7'109 and '9'109 to be primes.

PROG

(Python)

from sympy import isprime

print([i for i in range(800) if [isprime(int(j + str(i))) for j in '123456789'].count(True) == 4]) # Daniel Starodubtsev, Apr 11 2020

CROSSREFS

Sequence in context: A231012 A231007 A129916 * A004769 A224380 A125771

Adjacent sequences:  A032691 A032692 A032693 * A032695 A032696 A032697

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, May 15 1998

STATUS

approved

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Last modified October 28 13:26 EDT 2021. Contains 348329 sequences. (Running on oeis4.)