OFFSET
1,1
COMMENTS
For the first nine Carmichael numbers of the form k^3 + 1, the values of k + 1 are 13, 37, 139, 271, 4801, 7561, 12841, 14701, 678481 and only 14701 is not a prime number.
The sequence also includes: 32490089562753934948660824001, 782293837499544845175052968001, 611009032634107957276386802479001. - Daniel Suteu, Dec 25 2020
LINKS
G. Tarry, I. Franel, A. Korselt, and G. Vacca, Problème chinois, L'intermédiaire des mathématiciens 6 (1899), pp. 142-144.
Eric Weisstein's World of Mathematics, Carmichael Number.
EXAMPLE
2628073 is a term because it is a Carmichael number and 2628073 = 138^3 + 1.
PROG
(PARI) is_c(n) = { my(f); bittest(n, 0) && !for(i=1, #f=factor(n)~, (f[2, i]==1 && n%(f[1, i]-1)==1)||return) && #f>1 }
for(n=1, 1e10, if(is_c(k=n^3+1), print1(k, ", ")))
(PARI) lista(kmax) = {my(m); for(k = 2, kmax, f = factor(k); for(i = 1, #f~, f[i, 2] *= 3); m = k^3 + 1; fordiv(f, d, if(!(m % (d+1)) && isprime(d+1), m /= (d+1))); if(m == 1, print1(k^3 + 1, ", "))); } \\ Amiram Eldar, May 02 2024
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Altug Alkan, Dec 10 2015
EXTENSIONS
More terms from Alois P. Heinz, Dec 10 2015
a(10)-a(13) from Daniel Suteu, Dec 25 2020
a(14) from Daniel Suteu confirmed by Amiram Eldar, May 02 2024
STATUS
approved