OFFSET
1,2
COMMENTS
By the definition, a(1) = a(89) = 0.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Happy Number
Eric Weisstein's World of Mathematics, Unhappy Number
Wikipedia, Happy number
EXAMPLE
n| 0 1 2 3 4 5 6 7 8 9
-----------------------------------------------------------
2| 2 -> 4 -> 16 -> 37 -> 58 -> 89.
3| 3 -> 9 -> 81 -> 65 -> 61 -> 37 -> 58 -> 89.
4| 4 -> 16 -> 37 -> 58 -> 89.
5| 5 -> 25 -> 29 -> 85 -> 89.
6| 6 -> 36 -> 45 -> 41 -> 17 -> 50 -> 25 -> 29 -> 85 -> 89.
PROG
(PARI) f(n) = {my(d = digits(n)); sum(k=1, #d, d[k]^2); }
a(n) = {my(nb = 0, fn = n); while (! ((n == 1) || (n == 89)), n = f(n); nb++); nb; } \\ Michel Marcus, Feb 25 2018
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Seiichi Manyama, Feb 24 2018
STATUS
approved