A215805 Prime numbers p such that 10^p + 1 can be written in the form a^2 + 2*b^2.

5, 7, 13, 19, 29, 31, 43, 53, 61, 67, 71, 179, 239, 263, 269, 293

Offset

1,1

Comments

These numbers have no prime factors of the form 5 or 7 (mod 8) to an odd power.

Links

Table of n, a(n) for n=1..16.

Samuel S. Wagstaff, Jr., The Cunningham Project, Factorizations of 2^n-1, for odd n's < 1200.

Prog

(PARI) forprime(i=2, 100, a=factorint(10^i+1)~; has=0; for(j=1, #a, if(a[1, j]%8>4&&a[2, j]%2==1, has=1; break)); if(has==0&&i%2==1, print(i" -\t"a[1, ])))

Crossrefs

Cf. A000533, A001562, A062397, A215804.

Sequence in context: A215804 A274242 A163427 * A339692 A164567 A191046

Adjacent sequences: A215802 A215803 A215804 * A215806 A215807 A215808

Keyword

nonn

Author

V. Raman, Aug 23 2012

Extensions

5 more terms from V. Raman, Aug 29 2012

Status

approved