OFFSET
1,1
COMMENTS
If sigma((p-1)/2) is odd then p is of the form n^2+1.
LINKS
Filip Jevtic, Table of n, a(n) for n=1,..., 78.
MATHEMATICA
Select[Prime[Range[1700000]], DivisorSigma[1, (#-1)/2] == DivisorSigma[1, (#+1)/2]&] (* Harvey P. Dale, Jul 23 2011 *)
PROG
(PARI) for(n=2, 10^6, if(sigma((prime(n)-1)/2)==sigma((prime(n)+1)/2), print(prime(n))))
(Magma) [ p: p in PrimesInInterval(3, 30000000) | SumOfDivisors((p-1) div 2) eq SumOfDivisors((p+1) div 2) ];
CROSSREFS
KEYWORD
nonn
AUTHOR
Filip Jevtic (mm07006(AT)alas.math.rs), Dec 16 2009, Dec 19 2009
STATUS
approved