OFFSET
1,1
COMMENTS
First of four consecutive primes in A206280.
LINKS
Charles R Greathouse IV and Zak Seidov, Table of n, a(n) for n = 1..10783 (First 3400 terms from Charles R Greathouse IV)
FORMULA
Numbers m such that m^2 = Sum_{i=k..k+3} prime(i) for some k.
EXAMPLE
6 is a term because 6*6 = 5 + 7 + 11 + 13;
18 is a term because 18*18 = 324 = 73 + 79 + 83 + 89.
PROG
(PARI) lista(nn) = {pr = primes(nn); for (i = 1, nn - 3, s = pr[i] + pr[i+1] + pr[i+2] + pr[i+3]; if (issquare(s), print1(sqrtint(s), ", ")); ); } \\ Michel Marcus, Oct 02 2013
(PARI) is(n)=n*=n; my(p=precprime(n\4), q=nextprime(n\4+1), r, s); if(n < 3*q+p+8, r=precprime(p-1); s=n-p-q-r; ispseudoprime(s) && (s == precprime(r-1) || s == nextprime(q+1)), r=nextprime(q+1); s=n-p-q-r; ispseudoprime(s) && (s == precprime(p-1) || s == nextprime(r+1))) \\ Charles R Greathouse IV, Oct 02 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Jun 21 2003
EXTENSIONS
Corrected and extended by Don Reble, Nov 20 2006
STATUS
approved