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A060289 Number of distinct (non-overlapping) twin Harshad numbers whose sum is prime and where the 2nd Harshad is <= 10^n. 2
4, 5, 17, 53, 250, 1404, 9013 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence seems to be incorrect. Charles R Greathouse IV, Apr 03 2014

LINKS

Table of n, a(n) for n=1..7.

FORMULA

Generate the twin Harshads whose sum is prime. Count how many there are where the 2nd Harshad in the pair is <= a consecutive power of 10.

EXAMPLE

a(1)=4 because there are four pairs of Harshads whose sum is prime and the 2nd Harshad in the pair is <=10; these are 1+2=3, 3+4=7, 5+6=11, 9+10=19. 8+9=17 is not included because this pair overlaps 7+8=15, which also happens to be not prime. (Another sequence might include such overlapping pairs.)

PROG

(PARI) Niven(n)=n%sumdigits(n)==0

a(n)=my(t, s); for(k=1, 10^n, if(Niven(k), if(isprime(t+k), t=-10^n; s++); t=k)); s \\ Charles R Greathouse IV, Jan 23 2014

CROSSREFS

Cf. A060288, A005349, A060159.

Sequence in context: A061806 A119997 A010361 * A215024 A066879 A134750

Adjacent sequences:  A060286 A060287 A060288 * A060290 A060291 A060292

KEYWORD

more,nonn,base

AUTHOR

Enoch Haga, Mar 23 2001

STATUS

approved

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Last modified August 29 19:56 EDT 2014. Contains 246211 sequences.