1,1
Triangular(p) = p*(p+1)/2 (see A034953).
Table of n, a(n) for n=1..5.
a(2) = 3 because 3 is the least prime such that the following are two primes:
p1 = 3 * 4 / 2 + 1 = 7.
p2 = 7 * 8 / 2 + 1 = 29.
a(3) = 43 because 43 is the least prime such that the following are three primes:
p1 = 43 * 44 / 2 + 1 = 947.
p2 = 947 * 948 / 2 + 1 = 448879.
p3 = 448879 * 448880 / 2 + 1 = 100746402761.
Cf. A000040, A000217, A034953, A231847, A231988.
Sequence in context: A308645 A086889 A269909 * A059495 A174325 A290366
Adjacent sequences: A231986 A231987 A231988 * A231990 A231991 A231992
nonn,hard,more
Alex Ratushnyak, Nov 16 2013
approved
