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A157480 a(n) = least prime p such that p + prime(n) is a square. 5
2, 13, 11, 2, 5, 3, 19, 17, 2, 7, 5, 107, 23, 101, 2, 11, 5, 3, 257, 29, 71, 2, 17, 11, 3, 43, 41, 37, 467, 31, 17, 13, 7, 5, 47, 173, 167, 1601, 2, 23, 17, 719, 5, 3, 59, 701, 113, 2, 29, 347, 23, 17, 83, 5, 67, 61, 131, 53, 47, 43, 41, 31, 17, 13, 11, 7, 569, 239, 53, 227, 47, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
The difference between prime 3 and the square 16 is 13 which is prime and in the sequence.
MATHEMATICA
Table[p=Prime[n]; b=Ceiling[Sqrt[p]]; While[!PrimeQ[x=b^2-p], b++]; x, {n, 72}]
PROG
(PARI) g(n)= c=0; forprime(x=2, n, for(k=1, n^2, if(issquare(x+k)&&isprime(k),
print1(k", "); c++; break))); c
CROSSREFS
Sequence in context: A213825 A333493 A244932 * A342953 A355896 A213306
KEYWORD
nonn
AUTHOR
Cino Hilliard, Mar 01 2009
EXTENSIONS
Better definition and Mma program from Zak Seidov, Mar 14 2013
STATUS
approved

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Last modified May 20 11:25 EDT 2024. Contains 372712 sequences. (Running on oeis4.)