OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..500
MAPLE
istriangular:=proc(n) local t1; t1:=floor(sqrt(2*n)); if n = t1*(t1+1)/2 then return t1 ; else return -1; end if; end;
A034963 := proc(n)
add(ithprime(i), i=n..n+3) ;
end proc:
for n from 1 to 90000 do
ist := istriangular(A034963(n)) ;
if ist >= 0 then
printf("%d, ", ist) ;
end if;
end do: # R. J. Mathar, Jun 04 2013
MATHEMATICA
(Sqrt[8#+1]-1)/2&/@Select[Total/@Partition[Prime[Range[ 60000]], 4, 1], OddQ[ Sqrt[8#+1]]&] (* Harvey P. Dale, Apr 06 2016 *)
PROG
(C)
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define TOP (1ULL<<30)
int main() {
unsigned long long i, j, p1, p2, p3, r, s;
unsigned char *c = (unsigned char *)malloc(TOP/8);
memset(c, 0, TOP/8);
for (i=3; i < TOP; i+=2)
if ((c[i>>4] & (1<<((i>>1) & 7)))==0 /*&& i<(1ULL<<32)*/)
for (j=i*i>>1; j<TOP; j+=i) c[j>>3] |= 1 << (j&7);
for (p3=2, p2=3, p1=5, i=7; i < TOP; i+=2)
if ((c[i>>4] & (1<<((i>>1) & 7)))==0) {
s = p3 + p2 + p1 + i;
r = sqrt(s*2);
if (r*(r+1)==s*2) printf("%llu, ", r);
p3 = p2, p2 = p1, p1 = i;
}
return 0;
}
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, May 28 2013
STATUS
approved