1,2

Numbers n such that n*(n+1)/2-1 is a nonnegative nonprime. [From Juri-Stepan Gerasimov, May 04 2010]

Table of n, a(n) for n=1..72.

Index entries for linear recurrences with constant coefficients, signature (2,-1).

1 UNION A002808 UNION A169546.

Drop[Range[100], {2, 3}] (* Harvey P. Dale, May 05 2018 *)

(PARI) a(n)=if(n==1, 1, n+2) \\ Charles R Greathouse IV, Sep 02 2011

Sequence in context: A214084 A114143 A171526 * A020705 A081313 A227983

Adjacent sequences: A171460 A171461 A171462 * A171464 A171465 A171466

nonn,easy

Juri-Stepan Gerasimov, Dec 09 2009, Dec 15 2009

approved