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A137410 a(n)=((5^n)-3) / 2. 0
1, 11, 61, 311, 1561, 7811, 39061, 195311, 976561, 4882811, 24414061, 122070311, 610351561, 3051757811, 15258789061, 76293945311 (list; graph; refs; listen; history; internal format)
OFFSET

0,2

COMMENTS

Sequence generalized : a(n)=((A^n)-(B^r)/(A-B); A,B,r given integers.

Primes in this form are sometimes of interest.

Examples :

A=2;B=1;r=1 gives A000225 and A001348 primes in it;

A=3;B=1;r=1 gives A003462 and A028491 primes in it;

A=3;B=2;r=1 gives A058481 and A014224 primes in it;

A=4;B=1;r=1 gives A002450;

A=4;B=2;r=1 gives A083420;

A=4;B=2;r=2 gives A002446;

A=5;B=1;r=1 gives A003463 and A004061 primes in it;

A=5;B=2;r=1 gives A037577;

FORMULA

a(n)=((5^n)-3) / 2

CROSSREFS

Cf. A000225, A000040.

Sequence in context: A023298 A106992 A115565 * A199414 A156095 A068846

Adjacent sequences:  A137407 A137408 A137409 * A137411 A137412 A137413

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka (ctibor.zizka(AT)seznam.cz), Apr 15 2008

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Last modified February 15 16:56 EST 2012. Contains 205825 sequences.