OFFSET
1,1
COMMENTS
These 2^k - 1 numbers have no prime factors of the form 2 (mod 3) to an odd power.
LINKS
V. Raman, Table of n, a(n) for n = 1..121
Samuel S. Wagstaff, Jr., The Cunningham Project, Factorizations of 2^n-1, for odd n's < 1200
EXAMPLE
2^67 - 1 = 10106743618^2 + 3*3891344499^2 = 9845359982^2 + 3*4108642899^2
PROG
(PARI) for(i=2, 100, a=factorint(2^i-1)~; has=0; for(j=1, #a, if(a[1, j]%3==2&&a[2, j]%2==1, has=1; break)); if(has==0&&i%2==1, print(i" -\t"a[1, ])))
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
V. Raman, Aug 23 2012
STATUS
proposed