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A060291 Number of twin Harshads, including overlaps, whose sum is prime and where the 2nd Harshad is <= 10^n. 0
7, 8, 21, 60, 278, 1520, 9583 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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 <= to a consecutive power of 10

EXAMPLE

a(1)=7 because there are 7 pairs of Harshads whose sum is prime and the 2nd Harshad in the pair is <= 10; these are 1+2=3, 2+3=5, 3+4=7, 5+6=11, 6+7=13, 8+9=17, 9+10=19. (Another sequence does not permit overlapping Harshad numbers.)

CROSSREFS

Cf. A060288-A060290, A005349, A060159.

Sequence in context: A308926 A152043 A181585 * A132899 A051175 A322651

Adjacent sequences:  A060288 A060289 A060290 * A060292 A060293 A060294

KEYWORD

more,nonn,base

AUTHOR

Enoch Haga, Mar 24 2001

STATUS

approved

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Last modified July 19 12:49 EDT 2019. Contains 325159 sequences. (Running on oeis4.)