A116209 Numbers k such that k concatenated with k+7 gives the product of two numbers which differ by 7.

1, 13, 41, 653, 2287, 2723, 5491, 23240971, 26823191, 60249661, 1841968537, 2009317771, 3044234903, 3258336353, 8166731261, 9481619237, 1281071245505271100098621541, 1551605670846640136726379653

Offset

1,2

Comments

If k+7 has d digits, the concatenation is k//k+7 = 10^d*k+k+7 = m*(m+7), therefore k//k-1 = 10^d*k+k-1 = (m-1)*(m+8), so there is a large overlap with A116153. - R. J. Mathar, May 22 2026

Links

Table of n, a(n) for n=1..18.

Crossrefs

Cf. A116153, A116147, A116208, A116210, A116215, A116340.

Sequence in context: A332255 A201121 A116153 * A002673 A081301 A159527

Adjacent sequences: A116206 A116207 A116208 * A116210 A116211 A116212

Keyword

nonn,base

Author

Giovanni Resta, Feb 06 2006

Status

approved