A231989 Least prime p such that f(0),...,f(n) are all primes, where f(0) = p, then f(i+1) = triangular(f(i))+1.

3, 3, 43, 236367611, 31542795419

Offset

1,1

Comments

Triangular(p) = p*(p+1)/2 (see A034953).

Links

Table of n, a(n) for n=1..5.

Example

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.

Crossrefs

Cf. A000040, A000217, A034953, A231847, A231988.

Sequence in context: A086889 A368162 A269909 * A059495 A372423 A174325

Adjacent sequences: A231986 A231987 A231988 * A231990 A231991 A231992

Keyword

nonn,hard,more

Author

Alex Ratushnyak, Nov 16 2013

Status

approved