190 Jean-Marie De Koninck
13 224
the smallest Sastry number made up of five digits (see the number 6 099).
13 365
the 20th solution of φ(n) = φ(n + 1) (see the number 15).
13 367
the smallest prime factor of the Mersenne number 241 1 (Plana, 1863), whose
complete factorization is given by
241
1 = 13 367 · 164 511 353.
13 456
the only solution n
1012
of σ(n) = 2n + 89.
13 649
the 15th prime number pk such that p1p2 . . . pk + 1 is prime (see the number
379).
13 650
the second solution of φ(n + 1) = 4φ(n) (see the number 1 260).
13 691
the second prime number p such that 83p−1 1 (mod p2) (see the number
4 871).
13 775
the third number n such that n2+2 is powerful: here 13 7752+2 = 189 750 627 =
33 · 112 · 2412 (see the number 265).
13 783
the fifth number which does not produce a palindrome by the 196-algorithm
(see the number 196).
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