The arithmetic sequence, 1487, 4817, 8147, in which each of the terms increases by 3330, is unusual in two ways:
- each of the three terms are prime, and,
- each of the 4-digit numbers are permutations of one another.
There are no arithmetic sequences made up of three 1-, 2-, or 3-digit primes, exhibiting this property, but there is one other 4-digit increasing sequence.
What 12-digit number do you form by concatenating the three terms in this sequence?
In [1]:
from sympy import isprime
from collections import defaultdict
from itertools import combinations
primes = defaultdict(list)
for n in range(1001, 10000, 2):
if isprime(n):
key = ''.join(sorted(str(n)))
primes[key].append(n)
for key in primes:
for p, q in combinations(primes[key], 2):
r = q + (q - p)
if r in primes[key]:
print(f'{p}{q}{r}')
break
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