OFFSET
3,1
COMMENTS
An n-th order digital invariant is a number such that the sum of the n-th powers of the digits of n equals some number k and the sum of the n-th powers of the digits of k equals n. An Armstrong number is where n = k.
REFERENCES
David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, London, England, 1997, pp. 124, 155.
LINKS
Tim Johannes Ohrtmann, Table of n, a(n) for n = 3..45
Eric Weisstein's World of Mathematics, Invariant.
MATHEMATICA
Do[k = 1; While[ !(Apply[Plus, IntegerDigits[Apply[Plus, IntegerDigits[k]^n]]^n] == k && Apply[Plus, IntegerDigits[k]^n] != k), k++ ]; Print[k], {n, 3, 7}]
CROSSREFS
KEYWORD
hard,nonn,base
AUTHOR
Robert G. Wilson v, Aug 09 2002
EXTENSIONS
a(8)-a(27) from Tim Johannes Ohrtmann, Aug 27 2015
STATUS
approved