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A068435 Consecutive prime powers without a prime between them. 0
8, 9, 25, 27, 121, 125, 2187, 2197, 32761, 32768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Only 5 pairs are known to 10^14.

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

8=2^3, 9=2^3, there is no prime between 8 and 9.

25=5^2, 27=3^3, there is no prime between 25 and 27.

PROG

(PARI) ispp(x) = !isprime(x) && isprimepower(x);

lista(nn=50000) = {my(prec = 0); for (i=1, nn, if (ispp(i), if (! prec, prec = i, if (primepi(i) == primepi(prec), print1(prec, ", ", i, ", ")); prec = i; ); ); ); } \\ Michel Marcus, Aug 24 2019

CROSSREFS

Cf. A025475, A060846, A067871, A246547.

Sequence in context: A077599 A109097 A115645 * A302554 A124438 A124184

Adjacent sequences:  A068432 A068433 A068434 * A068436 A068437 A068438

KEYWORD

nonn,more,changed

AUTHOR

Jon Perry, Mar 09 2002

STATUS

approved

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Last modified August 25 13:50 EDT 2019. Contains 326324 sequences. (Running on oeis4.)