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A291340
Primes p such that phi(p*(p-1)/2) is a triangular number (A000217).
0
2, 617, 11243, 72817, 134213, 1083601, 1301617, 669175321, 2759347757, 5023245823, 10904836391, 11230923643, 12828977503, 27741297781
OFFSET
1,1
COMMENTS
Inspired by A291199.
PROG
(Python)
from __future__ import division
from sympy.ntheory.primetest import is_square
from sympy import totient, nextprime
A291340_list, p = [2], 3
while p < 10**6:
if is_square(8*(p-1)*totient((p-1)//2)+1):
A291340_list.append(p)
p = nextprime(p)
CROSSREFS
Sequence in context: A281537 A134796 A120830 * A332162 A364070 A046856
KEYWORD
nonn,more
AUTHOR
Chai Wah Wu, Aug 31 2017
STATUS
approved