OFFSET

1,1

COMMENTS

Also numbers k such that k concatenated with k+4 gives the product of two numbers which differ by 7.

Since k*(10^j+1) + 4 = m*(m+7) iff k*(10^j+1) - 4 = m*(m+7) - 8 = (m-1)*(m+8) = M*(M+9) this is trivially the same sequence. - N. J. A. Sloane, Apr 11 2007

EXAMPLE

8776//8772 = 9364 * 9373, where // denotes concatenation. Also 8776//8780 = 9365 * 9372.

CROSSREFS

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, Feb 06 2006

EXTENSIONS

Edited by N. J. A. Sloane, Apr 11 2007

STATUS

approved