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A124199 Primes of the form k(k+1)/2-2 (i.e., two less than triangular numbers). 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Equal to primes of the form (k^2-17)/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]]

PROG

(Python)

import sympy

[n*(n+1)/2-2 for n in range(10**6) if isprime(n*(n+1)/2-2)] # 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

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Last modified January 24 19:19 EST 2020. Contains 331211 sequences. (Running on oeis4.)