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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Inspired by A291199.

LINKS

Table of n, a(n) for n=1..14.

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

Cf. A000217, A291199.

Sequence in context: A281537 A134796 A120830 * A332162 A046856 A156938

Adjacent sequences:  A291337 A291338 A291339 * A291341 A291342 A291343

KEYWORD

nonn,more

AUTHOR

Chai Wah Wu, Aug 31 2017

STATUS

approved

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Last modified May 20 13:32 EDT 2022. Contains 353873 sequences. (Running on oeis4.)