A057978 Number of untouchable numbers <= 10^n.
2, 5, 89, 1212, 13863, 150232, 1574973, 16246940, 165826606, 1681871718, 16988116409, 171128671374
Offset: 1
Links
- K. Chum, R. K. Guy, M. J. Jacobson, Jr., and A. S. Mosunov, Numerical and statistical analysis of aliquot sequences, Experimental Mathematics (2018), pp. 1-12.
- Paul Pollack and Carl Pomerance, Some problems of Erdős on the sum-of-divisors function, Transactions of the American Mathematical Society, Series B Vol. 3, No. 1 (2016), pp. 1-26.
- Carl Pomerance and Hee-Sung Yang, Variant of a theorem of Erdős on the sum-of-proper-divisors function, Mathematics of Computation, Vol. 83, No. 288 (2014), pp. 1903-1913.
- Index entries for sequences related to numbers of primes in various ranges
Crossrefs
Cf. A005114.
Extensions
a(5)-a(6) from Donovan Johnson, Jul 19 2008
a(7) from Donovan Johnson, Aug 13 2011
a(8)-a(10) from Amiram Eldar; a(8) was taken from the paper by Pomerance and Yang, a(9)-a(10) were taken from the paper by Pollack and Pomerance
a(11)-a(12) added by Amiram Eldar, Sep 29 2018 from the paper by Chum et al.