A116935 Semiprimes (A001358) which are the concatenation of the numbers 1 through n for some n.

123, 1234, 1234567, 12345678910111213141516171819202122232425262728293031323334

Offset: 1

Author

Jonathan Vos Post, Mar 20 2006

Keywords

• base
• nonn
• less

Comments

Next term has 185 digits, and it is thus too large to be included. It is equal to the concatenation of the first 97 integers. - Giovanni Resta, Jun 15 2016

Examples

			a(1) = 123 = 3 * 41.
a(2) = 1234 = 2 * 617.
a(3) = 1234567 = 127 * 9721.
a(4) = 2 * 6172839455055606570758085909601061116212631364146515661667.
		

Crossrefs

Cf. A001358, A007908.

Formula

{A007908} intersect {A001358}.