A261066 a(n) = (7^(2^n) - 1) / 2^(n+2).

6, 150, 180150, 519264540150, 8628341205030630049260150, 4764689404827483203666304150636608674826622242700150

Offset

1,1

Comments

(m^(2^n)-1)/2^(n+2) is an integer for any odd value of m and n>0.

The next term, a(7), has 106 decimal digits.

Links

Table of n, a(n) for n=1..6.

Formula

a(n) == 150 (mod 10^4) for all n > 1. - M. F. Hasler, Aug 11 2015

Example

a(3) = (7^8 - 1)/2^5 = 180150.

Mathematica

Table[(7^(2^n) - 1)/2^(n + 2), {n, 1, 7}] (* Vincenzo Librandi, Aug 09 2015 *)

Prog

(PARI) first(m)=vector(m, i, (7^(2^i)-1)/2^(i+2)); /* Anders Hellström, Aug 08 2015 */
(Magma) [(7^(2^n)-1)/2^(n+2): n in [1..10]]; // Vincenzo Librandi, Aug 09 2015
(PARI) A261066(n)=7^2^n>>(n+2) \\ M. F. Hasler, Aug 11 2015

Crossrefs

Cf. A059723, A068531, A097421. Twice A359500.

Sequence in context: A232689 A165436 A378936 * A297737 A352757 A168654

Adjacent sequences: A261063 A261064 A261065 * A261067 A261068 A261069

Keyword

nonn

Author

Marco Ripà, Aug 08 2015

Extensions

a(5) corrected by Vincenzo Librandi, Aug 09 2015

Status

approved