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A280555 Primes p such that sigma(sigma(p)) is a Fibonacci number. 1
19289, 7391381, 9041581, 9124081, 9589141, 645617593711, 786881099503, 793374393583, 188950298985689, 215446003400539, 228846950929339, 257138974382029, 265666386165589, 276918720321829, 280481623844131, 323331286115017, 326905876894417 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Is this sequence infinite?

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

Prime number 7391381 is a term because sigma(sigma(7391381)) = 14930352 is a Fibonacci number.

PROG

(PARI) isFibonacci(n)=my(k=n^2); issquare(k+=(k+1)<<2) || (n>0 && issquare(k-8));

is(n)=isFibonacci(sigma(n+1))&&isprime(n);

CROSSREFS

Cf. A008333, A051027, A272412, A280545.

Sequence in context: A186875 A251803 A184667 * A031831 A252901 A126721

Adjacent sequences:  A280552 A280553 A280554 * A280556 A280557 A280558

KEYWORD

nonn

AUTHOR

Altug Alkan, Jan 05 2017

EXTENSIONS

Terms confirmed by Giovanni Resta, Jan 07 2017

STATUS

approved

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Last modified August 25 15:34 EDT 2019. Contains 326324 sequences. (Running on oeis4.)