OFFSET
0,2
COMMENTS
This is the root congruent to 2 mod 5.
REFERENCES
J. H. Conway, The Sensual Quadratic Form, p. 118.
K. Mahler, Introduction to p-Adic Numbers and Their Functions, Cambridge, 1973, p. 35.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1121
FORMULA
Successive values of 2^(5^x) mod 5^x. - Joe K. Crump (joecr(AT)carolina.rr.com), Jan 20 2001
MATHEMATICA
Table[ PowerMod[2, 5^n, 5^n], {n, 0, 24}] // Union (* Jean-François Alcover, Dec 03 2012, from formula given by Joe K. Crump *)
PROG
(PARI) sqrt(-1+O(5^40))
(PARI) {a(n) = local(k, x, y); for(i = 0, n, until( x != (y = truncate( sqrt( -1 + O(5^(k++))))), x = y)); x} /* Michael Somos, Mar 03 2008 */
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
STATUS
approved