OFFSET
1,5
COMMENTS
The n-th odd prime for which 5 is a square mod p is A038872(n).
REFERENCES
A. J. C. Cunningham, Quadratic Partitions. Hodgson, London, 1904, p. 1.
D. H. Lehmer, Guide to Tables in the Theory of Numbers. Bulletin No. 105, National Research Council, Washington, DC, 1941, p. 55.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
A. J. C. Cunningham, Quadratic Partitions, Hodgson, London, 1904. [Annotated scans of selected pages]
EXAMPLE
5 = (5^2 - 5*1^2)/4 so a(1)=1;
11 = (7^2 - 5*1^2)/4 so a(2)=1.
PROG
(PARI) a(n)=local(y, p); if(n<1, 0, p=0; y=1; until(p>=n, y++; if(issquare(5+O(prime(y))), p++)); p=prime(y); y=0; until(issquare(4*p+5*y^2), y++); y)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved