OFFSET
1,2
COMMENTS
Numbers m | 70^e with integer e >= 0. - Michael De Vlieger, Aug 22 2019
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = (2*5*7)/((2-1)*(5-1)*(7-1)) = 35/12. - Amiram Eldar, Sep 23 2020
a(n) ~ exp((6*log(2)*log(5)*log(7)*n)^(1/3)) / sqrt(70). - Vaclav Kotesovec, Sep 23 2020
MATHEMATICA
With[{n = 1120}, Sort@ Flatten@ Table[2^i * 5^j * 7^k, {i, 0, Log2@ n}, {j, 0, Log[5, n/2^i]}, {k, 0, Log[7, n/(2^i*5^j)]}]] (* Michael De Vlieger, Aug 22 2019 *)
PROG
(PARI) isok(n) = (n/(2^valuation(n, 2)*5^valuation(n, 5)*7^valuation(n, 7)) == 1); \\ Michel Marcus, Oct 01 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Douglas Winston (douglas.winston(AT)srupc.com), Jul 05 2005
STATUS
approved