OFFSET
1,1
COMMENTS
Triangular numbers n(n+1)/2 such that n and A073093(n+1) are both prime.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
3 has one prime factor; 1+1 = 2 is prime, hence 2*3/2 = 3 is in the sequence.
14 = 2*7 has two prime factors; 1+2 = 3 is prime, hence 13*14/2 = 91 is in the sequence.
24 = 2*2*2*3 has four prime factors; 1+4 = 5 is prime, hence 23*24/2 = 276 is in the sequence.
MATHEMATICA
aQ[n_] := PrimeQ[n] && PrimeQ[PrimeOmega[n + 1] + 1]; p = Select[Range[470], aQ]; p*(p + 1)/2 (* Amiram Eldar, Aug 31 2019 *)
PROG
(Magma) [ p*(p+1)/2: p in PrimesUpTo(490) | IsPrime(1 + &+[ f[2]: f in Factorization(p+1) ]) ];
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Dec 31 2008
EXTENSIONS
Edited, corrected (3 inserted) and extended beyond a(16) by Klaus Brockhaus, Jan 05 2009
3 inserted and extended by R. J. Mathar, Jan 03 2009
STATUS
approved