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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
OFFSET
1,1
LINKS
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 * A368374 A004769 A224380
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, May 15 1998
STATUS
approved