A116294 Numbers k such that k*(k+1) gives the concatenation of two numbers m and m+1.

3, 7, 78, 80919, 91809, 326510, 475025, 524975, 673490, 4323777, 4767132, 5232868, 5676223, 4083911141, 4975000250, 5024999750, 5916088859, 9503960496, 9604950396, 4186904462792, 4313465946775, 5686534053225, 5813095537208, 7504715871407, 7631277355390

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..2000

Example

80919 * (80919 + 1) = 6547965480, the concatenation of 65479 and 65479 + 1.

Mathematica

Union @@ ((x /. List@ ToRules@ Reduce[x (x+1) == 10^# y +y+1 && x>0 && 10^(#-1) <= y+1 < 10^#, {x, y}, Integers]) & /@ Range[13] /. x->{}) (* Giovanni Resta, Jul 08 2018 *)

Crossrefs

Cf. A116163, A116285, A116295, A116301.

Sequence in context: A364660 A219292 A181554 * A077793 A175236 A343763

Adjacent sequences: A116291 A116292 A116293 * A116295 A116296 A116297

Keyword

nonn,base

Author

Giovanni Resta, Feb 06 2006

Extensions

More terms from Giovanni Resta, Jul 08 2018

Status

approved