

A060291


Number of twin Harshads, including overlaps, whose sum is prime and where the 2nd Harshad is <= 10^n.


0




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. A060288A060290, 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



