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A255885 Smallest base b such that there exist exactly n Wieferich pseudoprimes (composites c satisfying b^(c-1) == 1 (mod c^2)) less than b. 5
17, 65, 145, 485, 649, 1297, 577, 2024, 5185, 8182, 7057, 8749, 14401, 30753, 56449, 57601, 77401, 129473, 51841, 129601, 254017, 296449, 202501, 389377 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..24.

PROG

(PARI) for(n=1, 10, b=2; while(b > 0, i=0; forcomposite(c=2, b, if(Mod(b, c^2)^(c-1)==1, i++)); if(i==n, print1(b, ", "); break({1})); b++))

(Python)

from itertools import count

from sympy import isprime

def A255885(n):

for b in count(1):

if n == sum(1 for c in range(2, b+1) if not isprime(c) and pow(b, c-1, c**2) == 1):

return b # Chai Wah Wu, May 18 2022

CROSSREFS

Cf. A244752, A252232, A255901.

Sequence in context: A086533 A226685 A108211 * A130885 A036545 A146807

Adjacent sequences: A255882 A255883 A255884 * A255886 A255887 A255888

KEYWORD

nonn,more

AUTHOR

Felix Fröhlich, Mar 09 2015

EXTENSIONS

a(20) from Chai Wah Wu, May 18 2022

a(21)-a(24) from Chai Wah Wu, May 19 2022

STATUS

approved

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Last modified December 8 20:46 EST 2022. Contains 358698 sequences. (Running on oeis4.)