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A083571 Numbers n such that A008509(n) is prime. 3
2, 3, 5, 10, 12, 72 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

P. 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: A050051 A252353 A241167 * 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

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Last modified May 28 07:01 EDT 2022. Contains 354112 sequences. (Running on oeis4.)