Those Fascinating Numbers 273

947 519

• the fifth solution of σ2(n) = σ2(n + 2) (see the number 1 079).

965 177

• the smallest number n which allows the sum

m≤n

1

σ(m)

to exceed 10 (see the

number 129).

968 760

• the smallest Niven number n such that n +70 is also a Niven number, but with

no others in between (see the number 28 680).

974 849

• the second prime factor of the Fermat number F11 =

2211

+ 1 (see the number

319 489).

987 631

• the largest prime number made up of exactly six distinct digits (see the number

9 871).

990 361

• the smallest number n requiring 13 iterations of the σI (n) function in order to

reach 1 (see the number 193).

990 409

• the fourth composite number n such that 2n−4 ≡ 1 (mod n); see the number

40 369.

999 983

• the largest six digit prime number.

1 000 003

• the smallest seven digit prime number.