A086247 Differences of successive 7-smooth numbers.

1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 1, 3, 1, 2, 1, 2, 2, 3, 1, 4, 2, 3, 3, 1, 1, 4, 2, 4, 3, 1, 6, 2, 3, 5, 1, 3, 6, 6, 2, 2, 5, 3, 4, 8, 5, 1, 2, 7, 5, 4, 3, 3, 10, 2, 6, 7, 5, 9, 3, 4, 4, 10, 6, 8, 1, 15, 3, 2, 5, 2, 4, 14, 10, 8, 6, 6, 15, 5, 4, 12, 7, 7, 10, 15, 3, 6, 8, 8, 5, 15, 12

Offset: 1

Author

Reinhard Zumkeller, Jul 13 2003

Keywords

• nonn
• look

Comments

A002473(n) is a term of A085153 iff a(n)=1.

Examples

			a(23) = 3 as A002473(23 + 1) - A002473(23) = 35 - 32 = 3. - _David A. Corneth_, Mar 31 2021
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Smooth Number

Crossrefs

Cf. A002473, A061987, A085153.

Programs

Mathematica

smooth7Q[n_] := n == Times@@({2, 3, 5, 7}^IntegerExponent[n, {2, 3, 5, 7}]);
Select[Range[1000], smooth7Q] // Differences (* Jean-François Alcover, Oct 17 2021 *)

Formula

a(n) = A002473(n+1) - A002473(n).