A083571 Numbers k such that A008509(k) is prime.

2, 3, 5, 10, 12, 72

Offset

1,1

Links

Table of n, a(n) for n=1..6.

Patrick De Geest, Subsets of palindromic triangulars

Mathematica

palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; t={}; c=0; Do[If[palQ[n*(n+1)/2], c=c+1; If[PrimeQ[n], AppendTo[t, c]]], {n, 10^3}]; t (* Jayanta Basu, May 14 2013 *)

Prog

(PARI) ispal(n)=n=digits(n); for(i=1, #n\2, if(n[i]!=n[#n+1-i], return(0))); 1
for(k=1, 1e9, if(ispal(k*(k+1)/2), n++; if(isprime(k), print1(n", ")))) \\ Charles R Greathouse IV, May 15 2013

Crossrefs

Cf. A008509, A050722, A008510, A050721.

Sequence in context: A252353 A241167 A385484 * A123090 A129281 A289536

Adjacent sequences: A083568 A083569 A083570 * A083572 A083573 A083574

Keyword

nonn,base,hard,more

Author

N. J. A. Sloane, Jun 14 2003

Status

approved