128 Jean-Marie De Koninck
1 429
the largest known number of the form 1 + 4p1p2 . . . pk: here
1429 =

1 + 4 · 2 · 3 · 5 · 7 · 11 · 13 · 17; the only known numbers of this form
are 3, 5, 11, 29 and 1 429;
the smallest prime number p such that p 1 and p + 1 each have exactly four
distinct prime factors: here 1 428 = 22 · 3 · 7 · 17 and 1 430 = 2 · 5 · 11 · 13 (see
the number 131).
1 430
the eighth Catalan number (see the number 14).
1 433
the smallest prime divisor of a Mersenne number (namely
2179
−1) which is such
that the following prime number, namely 1 439, is also a divisor of a Mersenne
number (namely
2719
1); the only other known prime number satisfying this
property is 6 079.
1 439
the smallest prime factor of the Mersenne number
2719
1, whose complete
factorization is given by
2719
1 = 1439 · 772207
·737572843389436536903316910033561929012829990389769 · P157.
1 441
the smallest number n 2 which is equal to the sum of the factorials of its
digits in base 15: here 1 441 = [6, 6, 1]15 = 6! + 6! + 1!; the only numbers with
this property are 1, 2, 1 441 and 1 442 (see the number 145).
1 442
the largest number which is equal to the sum of the factorials of its digits in
base 15: here 1 442 = [6, 6, 2]15 = 6! + 6! + 2! (see the number 1 441).
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