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A165319 Primes p where the number of divisors of p+1 is a power of 2. 3
2, 5, 7, 13, 23, 29, 37, 41, 53, 61, 73, 101, 103, 109, 113, 127, 137, 151, 157, 167, 173, 181, 193, 229, 257, 263, 269, 277, 281, 311, 313, 317, 353, 373, 383, 389, 397, 401, 409, 421, 433, 439, 457, 461, 487, 509, 541, 569, 593, 601, 613, 617, 631, 641, 653 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000

MAPLE

b:= proc(n) option remember; is(n=2^ilog2(n)) end:

a:= proc(n) option remember; local p; p:= `if`(n=1, 1, a(n-1));

      do p:= nextprime(p);

         if andmap(b, map(i-> i[2]+1, ifactors(p+1)[2])) then break fi

      od; p

    end:

seq(a(n), n=1..55);  # Alois P. Heinz, Sep 05 2019

PROG

(PARI) isok(p) = isprime(p) && (nd = numdiv(p+1)) && (nd == 2^valuation(nd, 2)); \\ Michel Marcus, Sep 05 2019

CROSSREFS

Cf. A165318, A165320.

Cf. A008329. [R. J. Mathar, Sep 20 2009]

Sequence in context: A261581 A045355 A252281 * A094712 A095281 A106889

Adjacent sequences:  A165316 A165317 A165318 * A165320 A165321 A165322

KEYWORD

nonn

AUTHOR

Leroy Quet, Sep 14 2009

EXTENSIONS

Extended by R. J. Mathar, Sep 20 2009

STATUS

approved

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Last modified January 22 16:29 EST 2020. Contains 331152 sequences. (Running on oeis4.)