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A053653
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Number of ways to rearrange digits of prime(n)*prime(n+1) to form a prime.
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2
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0, 0, 1, 0, 1, 0, 1, 2, 0, 0, 3, 4, 8, 0, 6, 11, 3, 0, 3, 6, 1, 1, 4, 3, 0, 2, 5, 6, 15, 15, 17, 16, 12, 12, 4, 10, 8, 5, 8, 18, 11, 23, 5, 13, 9, 10, 8, 6, 27, 9, 4, 6, 14, 4, 24, 3, 14, 6, 4, 33, 7, 14, 11, 12, 6, 86, 26, 53, 13, 79, 27, 51, 81, 61, 26, 39, 25, 54, 17, 25
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OFFSET
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1,8
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COMMENTS
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Leading zeros are not allowed in the rearranged number.
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LINKS
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EXAMPLE
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a(8) = 2 because 19*23 = 437 and 2 primes, 347 and 743, can be formed from the digits of 437.
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PROG
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(Python)
from sympy import isprime, prime
from sympy.utilities.iterables import multiset_permutations as mp
def c(s):
return sum(1 for t in mp(s) if t[0]!='0' and isprime(int("".join(t))))
def a(n): return c(str(prime(n)*prime(n+1)))
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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