A396019 Grand-grand-grand-kangaroo numbers: kangaroo numbers whose inner number is a grand-grand-kangaroo number (A395926).

131250000, 231250000, 331250000, 393750000, 431250000, 531250000, 631250000, 693750000, 731250000, 831250000, 911250000, 931250000, 956250000, 993750000, 1031250000, 1312500000, 2031250000, 2312500000, 3031250000, 3093750000, 3312500000, 3937500000, 4031250000

Offset

1,1

Links

David A. Corneth, Table of n, a(n) for n = 1..10472 (terms <= 10^45)

Michael S. Branicky, Python program for OEIS A396019

Carole Dubois, Graphs for Kangaroos

Mickaël Launay, Nombres kangourous, l’énigme maths du « Monde » nᵒ 97

Example

931250000 is a grand-grand-grand kangaroo number as a multiple of 3125000, 3125000 is itself a grand-grand kangaroo number as a multiple of 12500, 12500 is itself a grand kangaroo number as a multiple of 250 and 250 is a kangaroo number as a multiple of 5.

Prog

(Python)
def joey(n): return int(str(n)[1:-1]) if n > 99 else 0
def kangaroo(n): return n > 99 and (j:=joey(n)) > 0 and n%j == 0
def ok(n): return n > 9999999 and kangaroo(n) and kangaroo(j:=joey(n)) and kangaroo(jj:=joey(j)) and kangaroo(joey(jj))
# Michael S. Branicky, May 14 2026
(Python) # see linked program to produce b-file

Crossrefs

Cf. A395720, A395761, A395926.

Sequence in context: A147715 A395235 A251400 * A251281 A011577 A186573

Adjacent sequences: A396015 A396017 A396018 * A396020 A396021 A396022

Keyword

nonn,easy,base

Author

Carole Dubois, May 14 2026

Status

approved