

A124199


Primes of the form k(k+1)/22 (i.e., two less than triangular numbers).


4



13, 19, 43, 53, 89, 103, 151, 229, 251, 349, 433, 463, 593, 701, 739, 859, 1033, 1223, 1429, 1483, 1709, 1889, 1951, 2143, 2699, 3001, 3079, 3319, 3739, 4003, 4093, 4463, 4751, 5563, 5669, 6553, 7019, 7873, 8513, 9043, 10009, 10151, 10729, 11173, 11779
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OFFSET

1,1


COMMENTS

Equal to primes of the form (k^217)/8. Also equal to primes p such that 8*p+17 is a square.  Chai Wah Wu, Jul 14 2014


LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..2000.


EXAMPLE

The (first five triangular numbers)2 are: 1,1,4,8,13. So a(1)=13 is the first prime of this form.


MATHEMATICA

Pick[ #1, PrimeQ[ #1]]&[((1/2)*#1*(#1 + 1)  2 & ) /@ Range[180]]
Select[Accumulate[Range[250]]2, PrimeQ] (* Harvey P. Dale, Jun 07 2020 *)


PROG

(Python)
import sympy
[n*(n+1)/22 for n in range(10**6) if isprime(n*(n+1)/22)] # Chai Wah Wu, Jul 14 2014


CROSSREFS

Cf. A055472.
Sequence in context: A252021 A216101 A096455 * A119869 A272200 A106904
Adjacent sequences: A124196 A124197 A124198 * A124200 A124201 A124202


KEYWORD

easy,nonn


AUTHOR

Peter Pein (petsie(AT)dordos.net), Dec 07 2006


STATUS

approved



